fix(buffer): reject ZSTs and address allocator review comments

[gatesn]

Reject zero-sized buffer elements at construction with compile-time assertions. ZST support was previously inconsistent; rejecting these types prevents division-by-zero and pointer-distance failures without adding iterator or growth special cases. Empty buffers of non-ZST types remain supported. Six compile-fail doctests cover the independent construction paths.

Remove the generic raw-owner constructor. Typed Vec adoption takes its pointer and element count directly from the Vec and retains that Vec for destruction. External byte owners continue to use Bytes::from_owner at the call site, without adding a buffer API.

Address the allocator-stack review comments with field documentation, an explanation of the optional allocator, and tests for owner lifetime, allocator retention, empty/shared ownership, sliced-buffer growth, and alignment. The allocator representation, buffer layout, alignment policy, and allocation benchmarks are retained. Both iterator-extension implementations and the owned iterator match the merged baseline. This is a focused alternative to #9745.

Validation:

• cargo nextest run -p vortex-buffer --all-features: 874 tests passed.
• cargo test --doc -p vortex-buffer --all-features: 8 ordinary and 6 compile-fail doctests passed.
• cargo clippy -p vortex-buffer --all-targets --all-features: passed.
• Nightly formatting and git diff --check: passed.
• All 70 executed CI checks passed, including Miri, ASan, TSan, platform tests, builds, and documentation. The documentation job passed after retrying a lost self-hosted runner.
• Workspace clippy was blocked locally by the CUDA nvCOMP download; full CI linting passed.

Performance validation:

• Three serial alternating local comparisons against the allocator-stack baseline place all 20 measured interleave, batched i8 filter, and multiplication cases within 2% of baseline.
• The final Graviton NEON run matches develop: u64 multiplication 15.1 vs 15.3 µs; i64 and 16,384-row multiplication 17.1 vs approximately 17.3 µs. The earlier NEON slowdowns disappeared with the ZST ban.
• The complete final CodSpeed report passed with no reported regressions.

[codspeed-hq]

Merging this PR will improve performance by 11.82%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 3 improved benchmarks
✅ 2196 untouched benchmarks
⏩ 206 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	allocate_drop_arrow[0]	456.9 ns	402.7 ns	+13.45%
⚡	WallTime	mul_i32_nonnull_avx512	7.9 µs	7 µs	+11.64%
⚡	Simulation	allocate_drop_bytes[0]	575.7 ns	521.6 ns	+10.39%

Tip

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_{Comparing ngates/buffer-review-minimal (2a3f517) with develop (85b70cf)²}

Footnotes

1. 206 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on develop (5c8c397) during the generation of this report, so 85b70cf was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩