Add make-and-blit array helpers

[Yu-zh]

Summary

• add make-and-blit helpers backed by %fixedarray.make_with_blit and %fixedarray.make_with_init_blit
• keep unsafe intrinsic wrappers private and expose only checked public helpers where needed
• route Array/ArrayView/Bytes/FixedArray allocation-plus-blit paths through backend-specific helpers
• add focused benchmarks for FixedArray copy, fixed-to-array conversion, Array/ArrayView concat, and resize growth

Commit structure

• Add make-and-blit array helpers
• Use make-and-blit helpers in array copies
• Add make-and-blit array benchmarks

Validation

• moon info
• moon fmt
• moon check --target native --deny-warn
• moon check --target wasm --deny-warn
• moon test immut/array --target native --release
• moon test --target native --release
• moon test --target wasm --release
• git diff --check

Notes

• rebased onto origin/main at 7a6bcacc4359e0c26f0959161e14a4b44872d16d
• the previous native release CI crash in immut/array is not reproducible on the rebased branch; the focused package and full native release suite both pass locally

[coveralls]

Coverage Report for CI Build 4486

Coverage decreased (-0.005%) to 94.084%

Details

• Coverage decreased (-0.005%) from the base build.
• Patch coverage: 2 uncovered changes across 2 files (94 of 96 lines covered, 97.92%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
builtin/fixedarray_block.mbt	6	5	83.33%
builtin/uninitialized_array.mbt	11	10	90.91%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15872
Covered Lines:	14933
Line Coverage:	94.08%
Coverage Strength:	207096.69 hits per line

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💛 - Coveralls

[Yu-zh]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

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