moonbitlang / core / 1454

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Pull #2805

github

refactor(immut/sorted_set): Change Compare implementation to compare by size first

BREAKING CHANGE: The Compare trait implementation for SortedSet now compares
sets by size first before comparing elements lexicographically. This is a
semantic change from the previous behavior.

Previous behavior:
- Compared sets element-by-element lexicographically
- {1,2} > {3} because 3 > 2 (compared until one iterator exhausted)

New behavior:
- Compares by size first, then by elements if sizes are equal
- {1,2} > {3} because size(2) > size(1)
- Only compares elements lexicographically when sizes are equal

Rationale:
- More intuitive: larger sets are "greater than" smaller sets
- Performance: Size comparison is O(1), avoids unnecessary element iteration
- Consistency: Matches common set comparison semantics in other languages

Changes:
- Refactored iterator-based Eq and Compare implementations to generic.mbt
- Extracted InorderIterator to external_iterator.mbt
- Added comprehensive tests for both same-size and different-size comparisons
- Both implementations now use the external iterator for element traversal

Request for review:
This is a breaking change that affects anyone using Compare/ordering operations
on SortedSet. Please review whether this new semantic is acceptable.

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