ci: add llama example build (iOS) (#32)

## Description
Added a workflow to build llama example app on iOS.

### Type of change
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] Documentation update (improves or adds clarity to existing
documentation)

### Tested on
- [ ] iOS
- [ ] Android

### Testing instructions
<!-- Provide step-by-step instructions on how to test your changes.
Include setup details if necessary. -->

### Screenshots
<!-- Add screenshots here, if applicable -->

### Related issues
<!-- Link related issues here using #issue-number -->

### Checklist
- [x] I have performed a self-review of my code
- [x] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [x] My changes generate no new warnings

### Additional notes
<!-- Include any additional information, assumptions, or context that
reviewers might need to understand this PR. -->

Author: chmjkb

.github/workflows/build-ios-llama-example.yml

@@ -0,0 +1,45 @@
+name: Example app iOS build check
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - '.github/workflows/build-ios-llama-example.yml'
+      - '*.podspec'
+      - 'examples/llama/ios/**'
+      - 'examples/llama/package.json'
+  pull_request:
+    paths:
+      - '.github/workflows/build-ios-llama-example.yml'
+      - '*.podspec'
+      - 'examples/llama/ios/**'
+      - 'examples/llama/package.json'
+jobs:
+  build:
+    if: github.repository == 'software-mansion/react-native-executorch'
+    name: "Example app iOS build check"
+    runs-on: macos-latest
+    steps:
+      - name: Check out Git repository
+        uses: actions/checkout@v4
+        
+      - name: Install node dependencies
+        working-directory: examples/llama
+        run: yarn
+
+      - name: Install pods
+        working-directory: examples/llama/ios
+        run: pod install
+
+      - name: Build app
+        working-directory: examples/llama/ios
+        run: |
+          set -o pipefail && xcodebuild \
+            -workspace llama.xcworkspace \
+            -scheme llama \
+            -sdk iphonesimulator \
+            -configuration Debug \
+            -destination 'platform=iOS Simulator,name=iPhone 16 Pro' \
+            build \
+            CODE_SIGNING_ALLOWED=NO | xcbeautify
+