refactor(csharp): migrate to native setup-dotnet caching

Replace common-cache with native caching in C# actions for better
performance and maintainability.

csharp-build changes:
- Add cache: true and cache-dependency-path to setup-dotnet
- Remove redundant common-cache step
- Simplify restore logic, remove cache-hit conditionals

csharp-publish changes:
- Add cache: true and cache-dependency-path to setup-dotnet
- Remove redundant common-cache step
- Simplify restore logic, use step-security/retry for restore

Benefits:
- Native caching is more efficient and better maintained
- Reduces common-cache dependencies from 7 to 5 actions
- setup-dotnet handles NuGet package caching automatically
- Cleaner workflow without complex conditional logic

Phase 2 complete: Reduced common-cache usage from 11 to 5 actions.

csharp-publish/action.yml

@@ -161,28 +161,22 @@ runs:
       uses: actions/setup-dotnet@d4c94342e560b34958eacfc5d055d21461ed1c5d # v5.0.0
       with:
         dotnet-version: ${{ inputs.dotnet-version || steps.detect-dotnet-version.outputs.detected-version }}
-
-    - name: Cache NuGet packages
-      id: cache-nuget
-      uses: ivuorinen/actions/common-cache@0fa9a68f07a1260b321f814202658a6089a43d42
-      with:
-        type: 'nuget'
-        paths: '~/.nuget/packages'
-        key-files: '**/*.csproj,**/*.props,**/*.targets'
-        key-prefix: 'csharp-publish'
+        cache: true
+        cache-dependency-path: '**/*.csproj'
 
     - name: Restore Dependencies
-      shell: bash
-      env:
-        CACHE_HIT: ${{ steps.cache-nuget.outputs.cache-hit }}
-      run: |
-        set -euo pipefail
+      uses: step-security/retry@e1d59ce1f574b32f0915e3a8df055cfe9f99be5d # v3
+      with:
+        timeout_minutes: 10
+        max_attempts: ${{ inputs.max-retries }}
+        command: |
+          echo "Restoring .NET dependencies..."
+          dotnet restore --verbosity normal
 
-        # Always run dotnet restore to ensure project.assets.json is present
-        if [[ "$CACHE_HIT" == 'true' ]]; then
-          echo "Cache hit - running fast dotnet restore"
-        fi
-        dotnet restore
+    - name: Restore Complete
+      shell: bash
+      run: |
+        echo "Cache hit - skipping dotnet restore"
 
     - name: Build Solution
       shell: bash