chore: add e2e synced shared helpers

[ava-silver]

Stack 1 of 3 -- synced shared helpers → #709 fixture → #710 lifecycle test + workflow.

What does this PR do?

Adds the cross-repo e2e helper modules under e2e/helpers/, synced from serverless-ci/e2e/shared:

• exec.ts -- promisified command runner with bounded retries on transient cloud errors.
• lambda-verifier.ts -- runner-agnostic AWS Lambda config verifier (layers, redirected handler, DD_* env, tags); per-tool specifics come in through a config arg.
• lambda-telemetry-checker.ts -- polls the Datadog API for spans and logs carrying the workload identity.
• naming.ts -- run-id, name-prefix, and freshness-tag helpers.
• .gitattributes -- marks the four modules `linguist-generated` so they collapse in diffs.

Motivation

First of a stack splitting the e2e suite by review concern. These files are generated by the `serverless-ci` e2e-shared sync (source of truth lives there); isolating them keeps the reviewable substance out of the other PRs. Review here just confirms they match upstream.

Testing Guidelines

No behavior on their own -- exercised by the lifecycle test in #710.

Additional Notes

`DO NOT EDIT` -- regenerated by the sync. Changes belong in `serverless-ci/e2e/shared`.

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog

[ava-silver]

• chore: add e2e lifecycle test and workflow #710
• chore: add e2e lambda fixture #709
• chore: add e2e synced shared helpers #708 👈 (View in Graphite)
• main

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.32%. Comparing base (2ee29a2) to head (c926b03).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #708   +/-   ##
=======================================
  Coverage   78.32%   78.32%           
=======================================
  Files          13       13           
  Lines        1158     1158           
  Branches      357      357           
=======================================
  Hits          907      907           
  Misses        119      119           
  Partials      132      132           

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