refactor: improve Percy build verification process

[devin-ai-integration]

refactor: improve Percy build verification with centralized error handling

Summary

This PR refactors the Percy build verification process to make it more robust and maintainable. The main changes include:

New centralized error handling utility (percy-error.ts) that provides:

• Custom PercyError class with standardized error codes
• PercyResult<T> type for consistent success/failure handling
• withRetry utility with configurable exponential backoff
• Logging utilities (logDebug, logWarning, logError)
• Build status formatting (formatBuildStatus, isAlertWorthy)

Improved build ID extraction (read-build-number-from-logs.ts):

• Replaced fragile string parsing with regex-based extraction
• Added build ID validation
• New extractBuildIdWithDetails function with detailed result information

Simplified GitHub Actions workflow (e2e.yml):

• Extracted check_logs function for log analysis
• Created is_retryable_error function for retry logic
• Cleaner retry mechanism with dedicated functions

Better affected detection (e2e-affected/action.yml):

• Improved Percy token validation with helpful error messages
• Extracted helper functions for commit fetching
• Parallel execution of commit fetching operations

Updates since last revision

• Added tests to achieve 100% branch coverage (was 98.77%)
• Removed unnecessary nullish coalescing in isAlertWorthy function that created unreachable code
• Added test for non-Error thrown values in file read operations

Review & Testing Checklist for Human

This is a medium-risk change affecting critical CI/CD infrastructure. Please verify:

• Regex patterns: The build ID extraction patterns were changed from [^/]+\/[^/]+ (exactly 2 path segments) to .* (any segments). Verify this matches all expected Percy URL formats like https://percy.io/82a32315/web/skyux-integration-e2e/builds/41420284
• Retry logic in e2e.yml: The bash script changes should be tested with actual Percy failures to ensure retries work correctly
• Backward compatibility: The refactoring adds new module dependencies - verify existing workflows still function correctly

Recommended test plan:

1. Run the E2E workflow on a test PR to verify Percy integration works end-to-end
2. Manually trigger a scenario where Percy fails to verify retry logic
3. Check that build ID extraction works with various Percy URL formats

Notes

• All 188 tests pass with 100% code coverage (statements, branches, functions, lines)
• Lint checks pass
• CI checks for build, formatting, and unit tests all pass
• E2E test failures in CI are due to missing Percy tokens in the fork environment, not code issues

Link to Devin run: https://app.devin.ai/sessions/51b556e9f4df4de095b9c69e0b4b5641
Requested by: @bcmake

[devin-ai-integration]

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