feat: add cooldown format and improved visibility for skipped updates

[onemen]

closes #1690

Technical Refactor: npm.ts & Cooldown Visibility

I have performed a major refactor of npm.ts to support the new --format cooldown option while improving overall performance and code maintainability.

Key Changes:

• findTargetAndFallback: Introduced a single-pass reducer that filters and resolves both the target upgrade version and a cooldown fallback simultaneously. By iterating through available versions only once, it avoids multiple loops for filtering and sorting, making the detection of "cooldown-safe" versions significantly more efficient.
• toVersionResult: This new utility standardizes how raw resolution data is formatted into a VersionResult object. It wraps the target version with its publish time and, if a cooldown is active, attaches the fallback version and relevant metadata.
• Uniform Implementation: With these two functions, the implementation across all target functions is now uniform, significantly reducing boilerplate and improving readability.

PR Highlights:

• Enhanced Visibility: Added --format cooldown to display a dedicated "Skipped due to x-day cooldown" section in the terminal, listing version changes and release ages.
• Comprehensive Testing: Added new test cases to cooldown.test.ts to verify the logic and the new formatting output.
• Documentation:
  • Updated the --format options table in the README.md.
  • Added a detailed "Cooldown Formatting" section with usage examples to the README.md at the end of cooldown section.

@raineorshine,
Currently, this new format logic does not apply when options.json is used. Please let me know if you would like me to extend this support to the JSON output as well.

[onemen]

@raineorshine

this PR is ready for review