feat: add filter method to Maybe and update documentation and tests

[richecr]

This pull request introduces a new filter method to the Maybe type, enabling value filtering based on predicates for both object-oriented and functional/curried usage. The change is thoroughly documented and tested, and includes updates to configuration and scripts for improved test coverage requirements.

Maybe type enhancements

• Added a filter(fn: (value: T) => boolean): Maybe<T> method to the Maybe interface, with implementations for both Just and Nothing. This allows filtering values in a Maybe, returning Nothing if the predicate fails. [1] [2] [3]
• Introduced a curried filter helper for functional pipelines, enabling easy composition with other Maybe helpers.

Documentation improvements

• Expanded the documentation in docs/maybe/index.md to explain and provide examples for the new filter method and its curried usage. Includes common use cases like validation and parsing. [1] [2]

Testing

• Added comprehensive tests for the new filter functionality, covering direct usage, chaining, curried pipelines, and various scenarios. [1] [2]

Configuration and scripts

• Updated bunfig.toml to require 100% coverage for lines, functions, statements, and branches, and to skip test files from coverage calculations.
• Adjusted the test script in package.json to run tests without the coverage flag, since coverage is now controlled via config.