refactor(allocator/vec): re-order methods

[overlookmotel]

Pure refactor. Move simple getter / setter methods len, set_len, capacity, and bump towards the top of impl, after the constructor methods.

I find it clearer to have these simple methods in an easy-to-find place.

Does not change any code, just moves it.

[overlookmotel]

• perf(allocator/vec): reduce pointer maths in Vec::extend_desugared #11087
• perf(allocator/vec): Vec::extend_desugared set len only at end #11082
• refactor(allocator/vec): access len and cap fields via getters/setters #11081
• refactor(allocator/vec): re-order methods #11080 👈 (View in Graphite)
• perf(allocator/vec): remove SetLenOnDrop #11079
• refactor(allocator/vec): limit scope of #[expect(clippy::cast_possible_truncation)] #11074
• perf(allocator/vec): remove alloc_guard from RawVec::from_raw_parts_in + clarify safety docs #11073
• docs(allocator/vec): correct safety comments for RawVec::append_elements #11072
• refactor(allocator/vec): clarify comment #11071
• main

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #11080 will not alter performance

_{Comparing 05-16-refactor_allocator_vec_re-order_methods (aa76a16) with main (f0b76e8)}

Summary

✅ 36 untouched benchmarks

[overlookmotel]

Merge activity

• May 17, 6:15 AM EDT: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• May 17, 10:52 AM EDT: overlookmotel added this pull request to the Graphite merge queue.
• May 17, 11:00 AM EDT: Merged by the Graphite merge queue.