Lazily construct collection shrink candidates

[mizchi]

Defers construction of per-element shrink iterator chains until structural collection candidates have been exhausted. It also returns the empty Array/List candidate without traversing or copying the original collection.

For obtaining the first shrink candidate from a 10,000-element collection on native release:

Collection	Before	After
Array	767.83 µs	212.59 ns
List	811.98 µs	119.95 ns

This is currently stacked on #4149 because that PR establishes empty-first List shrinking. Once #4149 merges, this PR’s diff will reduce to the lazy construction change and its benchmark.

Validation: moon test quickcheck/shrink --target all, moon check --target all, and moon info.

[Copilot]

Pull request overview

Improves QuickCheck shrinking performance for large collections by deferring per-element shrink-chain construction until after structural (remove-chunk / empty) candidates are exhausted, while also reordering several shrink candidate streams to prefer simpler values (notably empty collections and zero) earlier.

Changes:

• Make Array/List shrinking return the empty candidate first without traversing/copying the original collection, and lazily construct sub-term shrink iterators.
• Reorder numeric/option shrink candidates to try simpler values first (e.g., 0/None earlier) and avoid duplicate 0 candidates for decimal shrinking.
• Add/adjust regression tests and add a benchmark test for first-candidate shrinking on 10k-element collections.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
quickcheck/shrink/utils.mbt	Adds fast-path empty Array candidate and removes duplicate decimal 0 candidates.
quickcheck/shrink/shrink.mbt	Reorders integer/BigInt/byte shrink candidates to prefer 0 first.
quickcheck/shrink/shrink_test.mbt	Updates snapshots for the new numeric shrink ordering and double shrink output.
quickcheck/shrink/composite.mbt	Reorders Option shrinking (None first) and defers Array sub-term shrink construction lazily.
quickcheck/shrink/composite_test.mbt	Updates snapshots to match new composite shrink ordering (option/result/array/tuples).
quickcheck/shrink/collection.mbt	Makes List shrinking emit empty first and defers length/sub-term shrink construction until needed.
quickcheck/shrink/collection_test.mbt	Updates collection shrink snapshots and adds a single-element list → empty regression test.
quickcheck/shrink_collection_bench_test.mbt	Adds benchmark tests for first shrink candidate on 10k-element Array/List.
quickcheck/README.mbt.md	Updates documentation example output to reflect new shrink ordering.
quickcheck/moon.pkg	Adds bench import for test-only benchmark compilation.
quickcheck/driver_test.mbt	Adds a regression test ensuring numeric shrinking reaches the boundary within default shrink budget.

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