feat(exp/simd): rewrite on go 1.27 portable simd package

[samber]

Summary

• Replace the go 1.26 simd/archsimd implementation (amd64-only, one hand-written kernel per instruction set, SIGILL hazard on CPUs without AVX2/AVX512) with go 1.27 portable stdlib simd package (amd64, arm64, wasm, plus a pure-Go emulated fallback everywhere else).
• Split each operation into a non-generic kernel (kernel.go, the only file importing "simd") and a generic wrapper, avoiding the midway compiler pass generics limitations.
• Min/Max/Clamp on float32/float64 now match lo.Min/lo.Max/lo.Clamp exactly on every architecture: NaN is detected cheaply and routed to the exact scalar algorithm instead of following architecture-dependent hardware NaN semantics; Clamp with mn > mx always returns mn on both the SIMD and scalar-fallback paths.
• Raise the exp/simd minimum Go version to 1.27.
• CI now tests go 1.26/1.27/stable on both amd64 and arm64 hardware, since the package is portable.
• Update the docs site (source refs, trimmed per-type signatures, examples) for the new API surface.

Test plan

• GOEXPERIMENT=simd go test -race ./... and GOEXPERIMENT=simd GODEBUG=simd=0 go test -race ./... (forced scalar fallback) both pass.
• Cross-compiled for darwin/arm64, linux/amd64, linux/arm64, linux/riscv64, linux/386, js/wasm, windows/amd64, plus the no-experiment stub build.
• golangci-lint run clean; -gcflags='-m' escape analysis confirms zero heap allocations in the hot kernels.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.87%. Comparing base (f728804) to head (c6f338e).
⚠️ Report is 23 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1005      +/-   ##
==========================================
+ Coverage   96.10%   98.87%   +2.77%     
==========================================
  Files          32       32              
  Lines        5520     4728     -792     
==========================================
- Hits         5305     4675     -630     
+ Misses        176       53     -123     
+ Partials       39        0      -39     

Flag	Coverage Δ
unittests	98.87% <ø> (+2.77%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.