test: add 64 integration and coverage tests for ValidationPipeline

Adds tests/test_pipeline_and_integration.py with 64 tests covering gaps
identified in the PeasyAI test suite:

- TestPipelineIntegration (7): Stage 1+2 end-to-end flow, inline-init
  fixed by post-processor, original_code preserved, validators_run list
- TestPipelineCustomisation (9): add/remove_validator, apply_fixes=False,
  include_test_validators, custom validator list
- TestPipelineResultAPI (9): errors/warnings properties, is_valid logic,
  summary format, to_review_dict shape and backward compat
- TestValidatePCodeConvenience (8): validate_p_code() and
  create_default_pipeline() helpers, full flow with is_test_file
- TestSyntaxValidatorBraceSemicolon (5): }; detection, auto-fix
- TestMachineStructureValidatorGoto (5): undefined/defined goto, self-
  loop, empty state INFO, multi-machine validation
- TestInputValidationResult (5): success()/failure() factory methods
- TestDesignDocValidatorEdgeCases (7): boundary lengths, all sections
  present, events mentioned, extract_metadata edge cases
- TestPipelineErrorHandling (3): crashing validator skipped gracefully,
  INFO issue recorded, other validators still run
- TestValidateFileAndProject (7): validate_file(), validate_project(),
  PTst path detection, cross-file DuplicateDeclarationValidator context

Co-authored-by: ankushdesai <12651260+ankushdesai@users.noreply.github.com>

Author: Copilot