Fix duplicate OPTIONS method error for paths with trailing slash

[abhishektang]

Description

Fixes#3816

This PR fixes the issue where enabling CORS on an API with paths that differ only by a trailing slash (e.g., /datasets and /datasets/) causes API Gateway to throw an error:

Duplicate method 'OPTIONS' found for resource /datasets. Only one is allowed. 

Problem

When CORS is enabled, SAM adds OPTIONS methods to all paths. However, API Gateway treats /path and /path/ as the same resource. If both paths exist in the template, SAM was adding OPTIONS to both separately, causing a duplicate method error.

Solution

The fix normalizes paths before adding CORS OPTIONS methods:

• Paths are normalized by removing trailing slashes (except for root /)
• Normalized paths are tracked in a set to skip duplicates
• Ensures only one OPTIONS method is added per normalized path

Changes

Modified files:

• samtranslator/model/api/api_generator.py: Added path normalization in _add_cors() method
• tests/model/api/test_api_generator.py: Added unit test test_add_cors_with_trailing_slash_paths

Testing

✅ Unit Tests

• Added new test test_add_cors_with_trailing_slash_paths that verifies:
  • Paths /datasets (POST) and /datasets/ (PUT) are correctly handled
  • Only one OPTIONS method is added (not duplicated)
  • Test passes successfully

✅ Integration Tests

• All 68 existing CORS integration tests pass without regression
• Verified no breaking changes to existing functionality

✅ Real-world Validation

• Tested with the production template from issue Bug: Duplicate method 'OPTIONS' error #3816
• Confirmed the fix resolves the duplicate OPTIONS error
• Template now transforms successfully

Related Issues

Closes#3816

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Checklist:

• Fixed on develop branch
• Added unit test for the fix
• All tests pass locally
• Tested with real-world production template
• No regressions in existing CORS tests
• Clear commit message
• Code follows project conventions