fix(ci): drop unneeded parens + use div_ceil on Rust 1.95 clippy gates

Two clippy-as-error issues blocking PR #184 CI:

1. `src/hpc/int8_tile_gemm.rs:147` (mine, from b1979d7) —
   `clippy::unused_parens` flagged the closure body `(((i*11+5) % 256)
   as u8 as i8)` in the `fallback_matches_scalar_reference_k64` test.
   The outer parens around the cast chain are redundant; rustfmt
   re-broke the line to multi-line after removal so it stays readable.

2. `tests/par_rayon.rs:9` (pre-existing) — `clippy::manual_div_ceil`
   flagged `(M + CHUNK_SIZE - 1) / CHUNK_SIZE`. Replaced with
   `M.div_ceil(CHUNK_SIZE)` per the clippy hint. This file was
   already in tree; the lint became active in clippy 1.95 (Rust
   stable) which CI now uses, so prior PRs weren't blocked by it
   but the rayon-features test build is now.

Both fixes are mechanical / no behaviour change:
  * `cargo clippy --tests --features rayon,native -- -D warnings`
    clean.
  * `cargo fmt --all --check` clean.

Stashed work-in-progress on the VPDPBUSD-zmm middle tier for
`matmul_i8_to_i32` (the natural symmetric next step after TD-T2,
analogous to the VDPBF16PS arm shipped in PR #182's
`bf16_gemm_dispatch`); will follow up in a separate commit once
CI is unblocked.

https://claude.ai/code/session_01HbqooFZHAjaUtFEzhA1R2u

Author: claude

src/hpc/int8_tile_gemm.rs

@@ -144,7 +144,7 @@ mod tests {
         // Deterministic pseudo-random inputs covering the u8 / i8 ranges.
         let a: Vec<u8> = (0..16 * k).map(|i| ((i * 7 + 3) % 256) as u8).collect();
         let b: Vec<i8> = (0..k * 16)
-            .map(|i| (((i * 11 + 5) % 256) as u8 as i8))
+            .map(|i| ((i * 11 + 5) % 256) as u8 as i8)
             .collect();
 
         let mut c_ref = vec![0i32; 256];

tests/par_rayon.rs

@@ -6,7 +6,7 @@ use ndarray::prelude::*;
 const M: usize = 1024 * 10;
 const N: usize = 100;
 const CHUNK_SIZE: usize = 100;
-const N_CHUNKS: usize = (M + CHUNK_SIZE - 1) / CHUNK_SIZE;
+const N_CHUNKS: usize = M.div_ceil(CHUNK_SIZE);
 
 #[test]
 fn test_axis_iter() {