Use blit for contiguous copies

[Yu-zh]

Summary

• use blit for contiguous copies in stable sort merge, bytes conversions/concat, deque linearization paths, and hash set copy
• add a small internal deque helper for copying the two physical views into a linear buffer
• avoid initialize-then-overwrite loops in the updated paths

Validation

• moon check builtin deque hashset --target all --target-dir /tmp/core-blit-pr-check
• moon test builtin deque hashset --target all --target-dir /tmp/core-blit-pr-test
• moon fmt
• moon info
• git diff --check

No .mbti files changed.

[coveralls]

Coverage Report for CI Build 4263

Coverage increased (+0.004%) to 94.641%

Details

• Coverage increased (+0.004%) from the base build.
• Patch coverage: 28 of 28 lines across 4 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15732
Covered Lines:	14889
Line Coverage:	94.64%
Coverage Strength:	218128.19 hits per line

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💛 - Coveralls

[Copilot]

Pull request overview

This pull request replaces several element-by-element copy loops with blit-based contiguous copies across core collection/bytes utilities to reduce overhead and avoid initialize-then-overwrite patterns, including in the stable-sort merge path.

Changes:

• HashSet: copy entries via FixedArray::blit_to instead of a manual loop.
• Deque: introduce a small internal unsafe_blit_to helper and use it in concat (+), copy, and realloc linearization paths.
• Bytes + stable sort: use make_uninit + UninitializedArray::unsafe_blit(_fixed) and bytes blit helpers for conversions/concat and TimSort merge buffering.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
hashset/hashset.mbt	Uses blit_to to copy the backing entries array when cloning a HashSet.
deque/deque.mbt	Adds an internal linearization blit helper and uses it for concat/copy/realloc copies.
builtin/bytes.mbt	Switches bytes-to-array conversions and bytes concatenation to blit-based copies.
builtin/array_sort_impl.mbt	Replaces merge-buffer construction/copy-back loops with UninitializedArray blit operations.

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