FFI: replace vx_string/vx_binary with vx_view

[myrrc]

vx_string/vx_binary is not a zero-copy abstraction. For every utf/binary view you allocate memory. This PR replaces both with a vx_view non-owning view akin to C++'s string_view.

[codspeed-hq]

Merging this PR will not alter performance

⚡ 3 improved benchmarks
❌ 2 regressed benchmarks
✅ 1602 untouched benchmarks
⏩ 42 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	chunked_varbinview_into_canonical[(1000, 10)]	170.1 µs	206.5 µs	-17.62%
❌	Simulation	compact[(4096, 90)]	750.6 ns	867.2 ns	-13.45%
⚡	Simulation	chunked_varbinview_canonical_into[(1000, 10)]	190.5 µs	153.9 µs	+23.72%
⚡	Simulation	chunked_varbinview_into_canonical[(100, 100)]	307.7 µs	272.5 µs	+12.93%
⚡	Simulation	bitwise_not_vortex_buffer_mut[128]	273.6 ns	244.4 ns	+11.93%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing myrrc/ffi-vxstr (deb614b) with develop (0d50342)²}

Footnotes

1. 42 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 (4abe3d0) during the generation of this report, so 0d50342 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[0ax1]

What is the value of splitting these types. It seems we now use str also for buffers that are just bytes.

[0ax1]

lgtm but lets rename to vx_view or span as discussed.