[Onyx] Replace ONE_ON_ONE_CHAT_REPORT_IDS derived value with a useOnyxState lookup

[sosek108]

Explanation of Change

This targets the Onyx store bump in Expensify#98956 and builds on the unmerged useOnyxState from react-native-onyx.

ONE_ON_ONE_CHAT_REPORT_IDS is an OnyxDerived index from participant set to the reportID of its 1:1 chat. It exists so the expense confirmation page can find the existing chat with the recipient without scanning every report when it mounts. That page is its only reader, but the engine keeps the index up to date on every report write for the whole life of the app, and writes it back into Onyx and to disk each time.

This removes the derived value. The page now asks useOneOnOneChatReportID for the one chat it needs. The hook reads the report collection and the session with useOnyxState, live, so the Search snapshot never applies, as before. The lookup walks the collection once per report write while the page is mounted, skips reports that do not contain both participants before running the 1:1 checks, and caches the answer on the collection snapshot, so the page's many re-renders between writes cost a map lookup. The answer is the same as the index: the first 1:1 or system chat in collection order with exactly those participants. While an optimistic DM and the real one share participants, the optimistic one stays the answer until it is removed, then the real one takes over. One edge case now follows getChatByParticipants rather than the order in which reports arrived: if a report earlier in the collection becomes a 1:1 chat for participants that a later chat already covers, the earlier one is returned. The config, its key and its type are removed. The persisted row is left on disk, as with the TODOS removal.

A new reassure test mounts the real confirmation page over 5,000 reports, unchanged on the base and on this branch. Mounting stays the same within noise (25.2 ms on the base, 25.7 ms here, after every report was replaced). Ten report writes with the page closed take 39 ms instead of 60 ms, and with the page open 202 ms instead of 211 ms. A first version that rebuilt the whole index on mount made the mount 40% slower, which is why the lookup searches for one chat instead.

Fixed Issues

$ https://github.com/callstack-internal/expensify-issues/issues/3079
PROPOSAL:

Tests

1. Sign in with an account that already has a 1:1 chat with another user (user B).
2. Create an expense from the global create button, enter an amount and pick user B.
3. On the confirmation page, submit. Verify the expense lands in the existing chat with user B and no second chat with user B appears in the LHN.
4. Start another expense and pick a user you never chatted with (user C). Submit. Verify a new chat with user C is created and opened.
5. Right away, start one more expense to user C and submit. Verify it goes into the same chat with user C, not a new one.
6. Open the IOU report with user B and add another expense from it. Verify the expense is added to that IOU report.

• Verify that no errors appear in the JS console

Offline tests

1. Go offline.
2. Create an expense to a user you never chatted with (user D) and submit. Verify an optimistic chat with user D appears.
3. Start a second expense to user D while still offline and submit. Verify it goes into the same optimistic chat.
4. Go back online. Verify both expenses end up in one chat with user D and no duplicate chat with user D remains in the LHN.

QA Steps

Same as tests.

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
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  • A similar style doesn't already exist
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• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
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  • I verified that all the inputs inside a form are aligned with each other.
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• If the PR adds or modifies the UI:
  • I asked an AI agent to review the changes for accessibility issues and addressed its findings.
  • I tested with a screen reader (VoiceOver on macOS) and verified all new/changed elements are reachable with a logical focus order.
  • I verified all new/changed elements have meaningful accessible names and roles.
  • I verified state changes are announced (e.g. checked/unchecked, expanded/collapsed, selected).
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

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