fix(simd): remove outdated nightly-only comment; add AVX-512 CI compile check (#494)

AVX-512 intrinsics (_mm512_*, _mm512_reduce_add_ps, _mm512_abs_ps) are
stable since Rust 1.72. The comment saying "requires nightly Rust" was
misleading — callers would skip the feature unnecessarily.

CI: add a compile-check build step with --features simd-avx512 on the
stable toolchain so regressions are caught. Runtime dispatch is already
in place (is_x86_feature_detected!("avx512f")); the build step verifies
the code at least compiles on runners that may lack AVX-512 hardware.

Closes #47

Co-authored-by: ruvnet <ruvnet@gmail.com>

.github/workflows/ruvector-postgres-ci.yml

@@ -229,6 +229,10 @@ jobs:
         run: cargo build --features pg17,index-all,quant-all,graph-complete --release
         working-directory: crates/ruvector-postgres
 
+      - name: Build with AVX-512 feature (compile-check on stable Rust)
+        run: cargo build --features pg17,simd-avx512 --release
+        working-directory: crates/ruvector-postgres
+
       - name: Test with all features
         run: cargo pgrx test pg17 --features index-all,quant-all,graph-complete
         working-directory: crates/ruvector-postgres

crates/ruvector-postgres/src/distance/simd.rs

@@ -22,9 +22,8 @@ use simsimd::SpatialSimilarity;
 // SIMD Feature Detection
 // ============================================================================
 
-/// Check if AVX-512F is available at runtime
-/// Note: AVX-512 intrinsics require nightly Rust, so this returns false on stable builds
-/// To enable AVX-512, compile with --features simd-avx512 on nightly Rust
+/// Check if AVX-512F is available at runtime.
+/// Requires compiling with `--features simd-avx512` (stable Rust 1.72+).
 #[cfg(target_arch = "x86_64")]
 #[inline]
 pub fn is_avx512_available() -> bool {