Refactor CollectingErrorsTest based on review feedback

- Add helper method overloads for all input types (File, InputStream, Reader)
  to eliminate inline catchThrowableOfType duplication
- Extract buildInvalidOrderJson() helper to avoid duplicated JSON building
  logic across 4 tests
- Use StandardCharsets.UTF_8 instead of checked exception "UTF-8" string
- Improve executor shutdown safety with shutdownNow() fallback and proper
  InterruptedException handling
- Enhance concurrent test to verify exact unique error values, catching any
  bucket-sharing regressions
- Use Files.deleteIfExists() for robust temp file cleanup
- Streamline hard failure test to focus on suppressed exception mechanics
- Replace hand-rolled try/catch blocks with expectDeferredBinding() helper
  in 4 additional tests

All 31 tests pass. Code is more maintainable with consistent patterns and
reduced duplication.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: sri-adarsh-kumar