Feat/add api guidelines fixed history (#23)

* Enhance `FixedHistory` with iterator support and documentation improvements

- Introduced `Iter` and `IntoIter` types for iterating over timestamps in most-recently-used (MRU) order, enhancing usability.
- Updated documentation to include detailed operation tables with method references, improving clarity and navigation.
- Added examples for the new iterator methods, demonstrating their usage in practical scenarios.
- Refined `FixedHistory` struct to derive `Copy`, ensuring lightweight copies in concurrent contexts.
- Implemented `PartialEq`, `Eq`, and `Hash` traits for `FixedHistory`, allowing logical content comparison and hashability.

* Enhance `FrequencyBuckets` with iterator support and documentation improvements

- Introduced `EntryIter` for iterating over all entries in `FrequencyBuckets`, yielding tracked entries in unspecified order.
- Updated documentation to include method references in the operations table, improving clarity and navigation.
- Added examples for the new `into_inner` method, demonstrating its usage in practical scenarios.
- Refined iterator implementations in `SlotArena` to enhance usability and maintain performance efficiency.

Author: TKorr