refactor: align CI workflow with ecosystem standards

- Add Swift version to cache keys to prevent version mismatch issues
- Add Package.swift validation step
- Add README verification tests step
- Add API breaking changes check step
- Improve cache isolation between Swift 6.0 and 6.2 builds
- Align workflow structure with swift-css-types standards

This ensures consistent CI validation across all type packages
and prevents issues from cached modules built with different
Swift versions.

Author: coenttb

.github/workflows/ci.yml

@@ -31,14 +31,26 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: ${{ runner.os }}-spm-${{ hashFiles('Package.swift') }}
+          key: ${{ runner.os }}-swift62-spm-${{ hashFiles('Package.swift') }}
           restore-keys: |
-            ${{ runner.os }}-spm-
+            ${{ runner.os }}-swift62-spm-
 
       # Note: swift test builds automatically, no separate build step needed
       - name: Test
         run: swift test -c debug
 
+      - name: Validate Package.swift
+        run: swift package dump-package
+
+      - name: Run README verification tests
+        run: swift test --filter ReadmeVerificationTests
+
+      - name: Check for API breaking changes
+        run: |
+          swift package diagnose-api-breaking-changes \
+            --breakage-allowlist-path .swift-api-breakage-allowlist || true
+        continue-on-error: true
+
   # Production validation: Latest Swift on Linux with release build
   linux-latest:
     name: Ubuntu (Swift 6.2, release)
@@ -51,8 +63,8 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: ${{ runner.os }}-spm-${{ hashFiles('Package.swift') }}
-          restore-keys: ${{ runner.os }}-spm-
+          key: ${{ runner.os }}-swift62-spm-${{ hashFiles('Package.swift') }}
+          restore-keys: ${{ runner.os }}-swift62-spm-
 
       # Note: swift test builds automatically in release mode
       - name: Test (release)
@@ -71,8 +83,8 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .build
-          key: ${{ runner.os }}-swift60-spm-${{ hashFiles('Package.swift') }}
-          restore-keys: ${{ runner.os }}-swift60-spm-
+          key: ${{ runner.os }}-swift60-compat-spm-${{ hashFiles('Package.swift') }}
+          restore-keys: ${{ runner.os }}-swift60-compat-spm-
 
       # Note: swift test builds automatically
       - name: Test (Swift 6.0)