Add comprehensive test suite and CI/CD setup

[trissim]

• Add 69 comprehensive tests covering all major functionality

  • SignatureAnalyzer tests for functions, methods, dataclasses
  • UnifiedParameterAnalyzer tests for unified API
  • DocstringExtractor tests for various docstring formats
  • Exception hierarchy tests
  • Public API and import tests

• Achieve 65% overall test coverage (92% for UnifiedParameterAnalyzer)

• Enhance GitHub Actions CI workflow

  • Add pip caching for faster builds
  • Separate lint job from test job
  • Add build verification job
  • Update to latest action versions (v4/v5)
  • Add support for develop branch
  • Set continue-on-error for linting to not block CI

• Update publish workflow

  • Add workflow_dispatch for manual triggers
  • Update to latest action versions
  • Add permissions for secure publishing

• Add comprehensive CONTRIBUTING.md guide

  • Development setup instructions
  • Testing guidelines
  • Code style requirements
  • Pull request process
  • Bug reporting template

• Update README.md

  • Add CI and PyPI badges
  • Add development section with setup instructions
  • Add testing instructions

• Fix bugs in source code

  • Fix DocstringInfo to always return dict for parameters (never None)
  • Fix parameter skipping logic to not skip regular function params
  • Add dunder field filtering for dataclasses
  • Handle callable objects properly in UnifiedParameterAnalyzer
  • Fix docstring_info.parameters access when docstring_info is None