ci(darwin): install ccache's runtime dylib deps (blake3, hiredis, xxhash, zstd)

Symptom (run 25634195866, job 75244019809): the Configure ccache step
on the Darwin llama-cpp build aborted with:

  dyld[5647]: Library not loaded: /opt/homebrew/opt/blake3/lib/libblake3.0.dylib
    Referenced from: /opt/homebrew/Cellar/ccache/4.13.5/bin/ccache
  Abort trap: 6

The previous Darwin fix (acc5588d) addressed missing /opt/homebrew/bin
symlinks after a brew cache restore by force-linking. This is a
different layer: ccache's Cellar dir IS restored from cache and IS
linked, but ccache 4.13 dynamically links against blake3 / hiredis /
xxhash / zstd at runtime, and those dependencies are NOT in the
restored Cellar paths. brew install ccache sees the ccache Cellar
present and skips the install — including skipping installation of
those transitive deps.

Two-part fix:
  - Add /opt/homebrew/Cellar/{blake3,hiredis,xxhash,zstd} to the brew
    cache restore/save paths so future cache-hit runs restore them.
  - Explicitly install + link them in the Dependencies step so even
    a fresh runner (cache miss on a new key) gets them, and brew has
    them on hand for ccache to dlopen.

Caught by run 25634195866. Pre-existing condition on Darwin runners;
surfaced because Darwin builds run more often after the llama-cpp-
darwin consolidation in #9731.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

.github/workflows/backend_build_darwin.yml

@@ -93,6 +93,10 @@ jobs:
             /opt/homebrew/Cellar/libomp
             /opt/homebrew/Cellar/llvm
             /opt/homebrew/Cellar/ccache
+            /opt/homebrew/Cellar/blake3
+            /opt/homebrew/Cellar/hiredis
+            /opt/homebrew/Cellar/xxhash
+            /opt/homebrew/Cellar/zstd
           key: brew-${{ runner.os }}-${{ runner.arch }}-v1-${{ hashFiles('.github/workflows/backend_build_darwin.yml') }}
 
       - name: Dependencies
@@ -100,13 +104,18 @@ jobs:
           # ccache is always installed (used by the llama-cpp variant build) so
           # the brew cache content stays stable across every backend in the
           # matrix — they all share one cache key.
-          brew install protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache
+          # blake3, hiredis, xxhash, zstd are ccache's runtime dylib deps.
+          # Without explicitly installing them, a brew cache-hit run restores
+          # ccache's Cellar dir but skips installing those transitive deps,
+          # and ccache fails at runtime with `dyld: Library not loaded:
+          # libblake3.0.dylib`.
+          brew install protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache blake3 hiredis xxhash zstd
           # The brew cache restores the Cellar dirs but NOT the bin symlinks
           # at /opt/homebrew/bin/*. brew install above sees the Cellar present
           # and decides "already installed" without re-linking, so on a cache-
           # hit run the formulas aren't on PATH. Force-link them; --overwrite
           # tolerates pre-existing symlinks from earlier installs.
-          brew link --overwrite protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache 2>/dev/null || true
+          brew link --overwrite protobuf grpc make protoc-gen-go protoc-gen-go-grpc libomp llvm ccache blake3 hiredis xxhash zstd 2>/dev/null || true
 
       - name: Save Homebrew cache
         if: github.event_name != 'pull_request' && steps.brew-cache.outputs.cache-hit != 'true'
@@ -121,6 +130,10 @@ jobs:
             /opt/homebrew/Cellar/libomp
             /opt/homebrew/Cellar/llvm
             /opt/homebrew/Cellar/ccache
+            /opt/homebrew/Cellar/blake3
+            /opt/homebrew/Cellar/hiredis
+            /opt/homebrew/Cellar/xxhash
+            /opt/homebrew/Cellar/zstd
           key: brew-${{ runner.os }}-${{ runner.arch }}-v1-${{ hashFiles('.github/workflows/backend_build_darwin.yml') }}
 
       # ---- ccache for llama.cpp CMake builds ----