refactor: simplify MFU cache policy and enhance documentation

[TKorr]

Updated the MFU cache policy to remove the unnecessary bucket_hint parameter, streamlining its usage. Adjusted related documentation and examples to reflect this change, improving clarity and consistency across the API. Additionally, added a validate_policy method in CacheBuilder to enforce policy constraints, ensuring better error handling and user guidance.

Description

Related Issue

Fixes #

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📝 Documentation update
• 🔧 Refactoring (no functional changes)
• ⚡ Performance improvement
• 🧪 Test addition or modification

How Has This Been Tested?

• Unit tests
• Integration tests
• Manual testing

Test environment:

• OS:
• Rust version:

Checklist

• My code follows the project's coding standards
• I have run cargo fmt and cargo clippy
• I have added tests for my changes
• All new and existing tests pass (cargo test)
• I have updated the documentation as needed
• I have added an entry to CHANGELOG.md (if applicable)

Screenshots (if applicable)

Additional Notes