Improve SortedSet union

[bobzhang]

Summary

• optimize union in SortedSet
• avoid re-counting elements by tracking size during tree copy/merge

Testing

• moon fmt
• moon info
• moon test

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https://chatgpt.com/codex/tasks/task_e_684bd59b9ccc8320b5e9a44429fe1b2b

[peter-jerry-ye-code-review]

Avoid duplicated tree copying in union operation

Category
Performance
Code Snippet
let (t1, _) = copy_tree_with_size(self.root)
let (t2, _) = copy_tree_with_size(src.root)
Recommendation
The size information from copy_tree_with_size is discarded but could be useful. Consider using it to initialize the base size before merging.
Reasoning
The initial size information could provide a better starting point for size tracking and potentially avoid some computations during the merge process.

Missing documentation for copy_tree_with_size function

Category
Maintainability
Code Snippet
fn[V] copy_tree_with_size(node : Node[V]?) -> (Node[V]?, Int)
Recommendation
Add detailed documentation explaining the purpose, parameters and return values using the ///| format as seen in other functions.
Reasoning
Consistent documentation helps maintainability and makes the codebase more approachable for new developers.

Potential integer overflow risk in size calculations

Category
Correctness
Code Snippet
(Some(new_node), lsize + rsize + 1)
Recommendation
Consider adding size overflow checks when adding node counts, or document the maximum supported set size.
Reasoning
The recursive addition of sizes could potentially overflow for very large sets, leading to incorrect size tracking.

[coveralls]

Pull Request Test Coverage Report for Build 7263

Details

• 16 of 16 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 93.115%

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Totals
Change from base Build 7259:	0.005%
Covered Lines:	8575
Relevant Lines:	9209

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💛 - Coveralls