test(aws_lambda): Add ARM64 architecture support for local Lambda testing

[ericapisani]

Configure SAM Lambda functions to match the host CPU architecture, preventing slow x86_64 emulation on ARM machines like macOS.

Also removes test_timeout_error which is a subset of test_timeout_error_scope_modified, reducing test run time.

Refs PY-2641

[linear-code]

PY-2641

[github-actions]

Codecov Results 📊

✅ 98900 passed | ⏭️ 6479 skipped | Total: 105379 | Pass Rate: 93.85% | Execution Time: 356m 52s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -4
Passed Tests	📉 -4
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2505 uncovered lines.
✅ Project coverage is 89.94%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.92%    89.94%    +0.02%
==========================================
  Files          193       193         —
  Lines        24896     24896         —
  Branches      8978      8978         —
==========================================
+ Hits         22386     22391        +5
- Misses        2510      2505        -5
- Partials      1430      1431        +1

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