Migrate BtreeRangeIter to BtreeCursorRange

[cberner]

Summary

This PR removes the BtreeRangeIter implementation and migrates all usages to the BtreeCursorRange type, consolidating the range iteration logic into a single implementation.

Key Changes

• Removed from btree_iters.rs:

  • BtreeRangeIter<K, V> struct definition and all its implementations
  • Helper methods: is_leaf() and get_entry() from RangeIterState
  • Iterator trait implementations (Iterator and DoubleEndedIterator)
  • Initialization and state management methods (new, new_inner, close, advance, etc.)

• Updated imports and usages:

  • Removed BtreeRangeIter from public exports in tree_store/mod.rs
  • Updated multimap_table.rs to use BtreeCursorRange instead of BtreeRangeIter in:
    • ValueIterState enum variant
    • MultimapValue::new_subtree() and new_subtree_free_on_drop() method signatures
    • All instantiation calls throughout the file (6 locations)

Implementation Details

The migration consolidates range iteration functionality by replacing the standalone BtreeRangeIter with BtreeCursorRange, which provides equivalent bidirectional iteration capabilities. The RangeIterState enum remains but with reduced helper methods, as the iteration logic is now centralized in BtreeCursorRange.

https://claude.ai/code/session_01FjAnvpv4K1pPnshfkNX7Pn

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.33%. Comparing base (6408c74) to head (4ffb4a8).

Files with missing lines	Patch %	Lines
src/multimap_table.rs	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1253      +/-   ##
==========================================
+ Coverage   88.10%   88.33%   +0.22%     
==========================================
  Files          36       36              
  Lines       15220    15022     -198     
==========================================
- Hits        13409    13269     -140     
+ Misses       1811     1753      -58     

Files with missing lines	Coverage Δ
src/tree_store/btree_iters.rs	91.92% <ø> (+6.33%)	⬆️
src/multimap_table.rs	84.26% <87.50%> (ø)

... and 4 files with indirect coverage changes

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