`buffer.memcmp` returns `true` when two byte buffers have identical length and
contents.
Reference CPU implementation:
```rust
let equal = a == b;
```
WGSL spelling note: lanes compare `(a[idx] & 0xffu) == (b[idx] & 0xffu)` and
reduce mismatches to a boolean result. This variant is not constant-time. Crypto
callers should use a separate constant-time comparison op that avoids early
exit and data-dependent timing.