chore: modernize repository for new maintainers

[DrBlury]

Summary

Comprehensive modernization of the codebase to prepare for new maintainers, including updated dependencies, strict TypeScript, CI/CD, expanded test coverage, and improved developer experience.

Changes

Dependencies & Build

• Update TypeScript to 5.7.2 with strict mode enabled
• Update ESLint to 9.x with flat config format
• Update Mocha to 11.0.1 with c8 for coverage reporting
• Update Prettier to 3.4.2 with best practices config
• Update all other dependencies to latest versions

CI/CD

• Add GitHub Actions workflow for CI (Node 18.x, 20.x, 22.x)
• Add Codecov integration for coverage reporting
• Add markdownlint check to CI pipeline
• Add format check to CI pipeline

Code Quality

• Enable TypeScript strict mode and fix all 45+ type errors
• Remove all explicit 'any' types with proper type definitions
• Fix runtime bugs:
  • Regex lastIndex state bug in rename functionality
  • Deprecated substr() usage
  • Unsafe non-null assertions

Testing

• Expand test suite from 5 to 85 tests
• Add proto3Primitive.test.ts (15 tests)
• Add proto3Import.test.ts (22 tests)
• Add proto3RenumberLogicExtended.test.ts (43 tests)
• Achieve ~95% coverage on tested modules

Developer Experience

• Add Husky pre-commit hooks with lint-staged
• Add markdownlint configuration and fix all markdown files
• Add CONTRIBUTING.md with development guidelines
• Update CHANGELOG.md with 0.5.7 section
• Add badges to README (CI status, coverage, marketplace)

Documentation

• Update README with proper markdown formatting
• Add contribution guidelines
• Document all major changes in CHANGELOG