chore(keyring): enhance package.json config for quality and enterprise readiness

[Wbaker7702]

This PR enhances the @enkryptcom/keyring package's package.json file for better maintainability, enterprise readiness, and developer experience.

Key improvements:

• Added homepage, bugs, and keywords fields for improved documentation and discoverability
• Enhanced exports for better module resolution and tree-shaking
• Added missing and updated types, typesVersions, and sideEffects configuration
• Updated node engine requirement to >=18.0.0
• Extended scripts for development, lint, formatting, and test coverage
• Added @vitest/coverage-v8 to devDependencies
• Improved dev tooling scripts for type-checking and coverage
• Tidied up ordering and clarity

Please review and merge to improve the package's maintainability and usage.

Resolves #<issue_number_if_applicable>.