fix: use rolling cache key for clcache on Windows to get cache hits

The static key caused clcache to restore a stale entry after every MSVC
runner update, resulting in 0 hits / 701 misses on every build run. A
sha-based key with a prefix restore-keys fallback and save-always mirrors
the rolling strategy used by ccache-action on Linux/macOS.

https://claude.ai/code/session_01XTvMZtPH8WpuiRBZkqWiHk

Author: claude

.github/workflows/build.yml

@@ -76,7 +76,10 @@ jobs:
         uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:
           path: ${{ github.workspace }}\.clcache
-          key: ${{ github.job }}-${{ matrix.platform }}
+          key: ${{ github.job }}-${{ matrix.platform }}-${{ github.sha }}
+          restore-keys: |
+            ${{ github.job }}-${{ matrix.platform }}-
+          save-always: true
 
       - name: Create sbom, binary & package
         env: