ci: complete the conda toolchain deps and add compiler + CPM caching

conda's llvmdev pulls runtime-only libzlib/libxml2 (no headers), so the
LLVM config's find_package(ZLIB)/find_package(LibXml2) came up empty on
Windows, which has no system fallback (Linux was masked by the runner's
system dev packages). Add zlib/zstd/libxml2-devel to the toolchain env so
the transitive imported targets (ZLIB::ZLIB, LibXml2::LibXml2) resolve on
both platforms.

Also cache the compiler output and dependency downloads: ccache (Linux)
and sccache (Windows) via CMAKE_<LANG>_COMPILER_LAUNCHER, plus a
CPM_SOURCE_CACHE so the CPM libraries are not re-downloaded each run.

Author: PearCoding

.github/workflows/build-linux.yml

@@ -38,9 +38,18 @@ jobs:
             llvmdev=20.1
             clangdev=20.1
             lld=20.1
+            zlib
+            zstd
+            libxml2-devel
           init-shell: bash
           cache-environment: true
 
+      - name: Setup ccache
+        uses: hendrikmuhs/ccache-action@v1.2
+        with:
+          key: ${{ github.job }}-${{ runner.os }}
+          max-size: 2G
+
       - name: Cache AnyDSL toolchain (thorin/artic/runtime)
         uses: actions/cache@v4
         with:
@@ -49,20 +58,31 @@ jobs:
           restore-keys: |
             anydsl-deps-${{ runner.os }}-
 
+      - name: Cache CPM sources
+        uses: actions/cache@v4
+        with:
+          path: .cpm-cache
+          key: cpm-${{ runner.os }}-${{ hashFiles('cmake/Dependencies.cmake') }}
+          restore-keys: |
+            cpm-${{ runner.os }}-
+
       - name: Generate CI setup config
         shell: bash -el {0}
         run: |
           pwsh -NoProfile -Command '
             $cfg = Get-Content scripts/setup/config.json -Raw | ConvertFrom-Json
             $cfg.LOCATION = "$env:GITHUB_WORKSPACE/deps"
             $cfg.LLVM.SYSTEM_DIR = "$env:CONDA_PREFIX"
+            $cfg.CMAKE.EXTRA_ARGS += "-DCMAKE_C_COMPILER_LAUNCHER=ccache"
+            $cfg.CMAKE.EXTRA_ARGS += "-DCMAKE_CXX_COMPILER_LAUNCHER=ccache"
             $cfg | ConvertTo-Json -Depth 16 | Set-Content scripts/setup/config.ci.json
           '
 
       - name: Setup dependencies and build Ignis
         shell: bash -el {0}
         run: |
           export CMAKE_PREFIX_PATH="$CONDA_PREFIX:$CMAKE_PREFIX_PATH"
+          export CPM_SOURCE_CACHE="$GITHUB_WORKSPACE/.cpm-cache"
           pwsh ./scripts/setup/setup.ps1 -config_file scripts/setup/config.ci.json
 
       - name: Run tests

.github/workflows/build-windows.yml

@@ -30,9 +30,19 @@ jobs:
             llvmdev=20.1
             clangdev=20.1
             lld=20.1
+            zlib
+            zstd
+            libxml2-devel
           init-shell: powershell
           cache-environment: true
 
+      - name: Setup sccache
+        uses: hendrikmuhs/ccache-action@v1.2
+        with:
+          variant: sccache
+          key: ${{ github.job }}-${{ runner.os }}
+          max-size: 2G
+
       - name: Cache AnyDSL toolchain (thorin/artic/runtime)
         uses: actions/cache@v4
         with:
@@ -41,6 +51,14 @@ jobs:
           restore-keys: |
             anydsl-deps-${{ runner.os }}-
 
+      - name: Cache CPM sources
+        uses: actions/cache@v4
+        with:
+          path: .cpm-cache
+          key: cpm-${{ runner.os }}-${{ hashFiles('cmake/Dependencies.cmake') }}
+          restore-keys: |
+            cpm-${{ runner.os }}-
+
       - name: Generate CI setup config
         shell: pwsh
         run: |
@@ -54,12 +72,15 @@ jobs:
           # prefix on the search path for every sub-build that re-runs
           # find_package(LLVM) via thorin.
           $cfg.CMAKE.EXTRA_ARGS += "-DCMAKE_PREFIX_PATH=$env:CONDA_PREFIX/Library"
+          $cfg.CMAKE.EXTRA_ARGS += "-DCMAKE_C_COMPILER_LAUNCHER=sccache"
+          $cfg.CMAKE.EXTRA_ARGS += "-DCMAKE_CXX_COMPILER_LAUNCHER=sccache"
           $cfg | ConvertTo-Json -Depth 16 | Set-Content scripts/setup/config.ci.json
 
       - name: Setup dependencies and build Ignis
         shell: pwsh
         run: |
           $env:CMAKE_PREFIX_PATH = "$env:CONDA_PREFIX/Library;$env:CMAKE_PREFIX_PATH"
+          $env:CPM_SOURCE_CACHE = "$env:GITHUB_WORKSPACE/.cpm-cache"
           ./scripts/setup/setup.ps1 -config_file scripts/setup/config.ci.json
 
       - name: Run tests