feat: switch metadata reads to compiled_contracts_metadata

[marcocastignoli]

Important

Do not merge until all three are checked — this PR removes the only fallback to sourcify_matches.metadata:

• Production backfill finished (backfill-compiled-contracts-metadata.mjs)
• --verify reports missingRows=0
• compiled_contracts_metadata added to the Datastream mirror (sourcify-matches stream)

Summary

Release 2 of 2 for #2924, stacked on #2941. Reads switch to the side table, writes to the old column stop:

• STORED_PROPERTIES_TO_SELECTORS (metadata, std_json_output) now read compiled_contracts_metadata; the table is LEFT JOINed only when one of those fields is requested, and grouped by its PK where a GROUP BY exists (PK grouping is what makes the json column selectable).
• getSourcifyMatchByChainAddress selects metadata via the same join.
• getCompilationsByIds (similarity search) joins the side table directly on the compilation PK — the LATERAL detour through sourcify_matches that The same metadata is stored 8.5 times over: ~139 GB of a 182 GB table #2924 called out is gone, along with its stale-compilation quirk.
• insertSourcifyMatch / updateSourcifyMatch no longer take or write metadata; the column stays in place (nullable, unread) until the drop.
• Tests read metadata from the side table; assertContractSaved's duplicate check collapses back into one query.

After this deploys, the remaining ops task is dropping sourcify_matches.metadata and reclaiming the ~139 GB with pg_repack.

Notes

• Will need a rebase once feat: store metadata once per compilation in compiled_contracts_metadata #2941 squash-merges into staging (GitHub retargets the base automatically).
• Local runs against the docker DB: storageServices 8 ✔, apiPrivate 6 ✔, verification-cases 38 ✔, apiv2 116 ✔.

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