save and load max_record_size and leaf_page_size for bftrees

[backurs]

This is a small PR, which builds upon an internal PR where we started implementing save/load functionality for bftrees. Since we recently bumped up bftree version to 0.4.7, which implements getter functions for max_record_size and leaf_page_size, we can save and load these variables when saving and load bftrees. This is necessary to do because we might need to increase max_record_size and leaf_page_size if the dimensionality of the vectors is too large

[Copilot]

Pull request overview

This PR enhances the BfTree save/load functionality by adding support for persisting and restoring the max_record_size and leaf_page_size configuration parameters. This builds upon previously implemented save/load infrastructure and leverages new getter functions available in bftree version 0.4.7.

Changes:

• Introduced BfTreeParams struct to encapsulate BfTree configuration parameters (bytes, max_record_size, leaf_page_size)
• Updated SavedParams and QuantParams to use BfTreeParams instead of simple usize values
• Modified load functions to restore BfTree configurations with saved max_record_size and leaf_page_size values
• Updated tests to demonstrate save/load of BfTree configurations

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.00%. Comparing base (48b9af8) to head (0c02ecd).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #724      +/-   ##
==========================================
- Coverage   89.01%   89.00%   -0.02%     
==========================================
  Files         428      428              
  Lines       78151    78235      +84     
==========================================
+ Hits        69566    69630      +64     
- Misses       8585     8605      +20     

Flag	Coverage Δ
miri	89.00% <ø> (?)
unittests	89.00% <ø> (?)

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