ci: add custom CodeQL workflow with conformance/ excluded

Author: alexhancock

.github/codeql/codeql-config.yml

@@ -0,0 +1,4 @@
+name: "CodeQL config"
+
+paths-ignore:
+  - conformance

.github/workflows/codeql.yml

@@ -0,0 +1,36 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: '0 0 * * 1' # Weekly on Monday
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      contents: read
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [rust, javascript-typescript, python, actions]
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: ${{ matrix.language }}
+          config-file: ./.github/codeql/codeql-config.yml
+
+      - name: Autobuild
+        uses: github/codeql-action/autobuild@v3
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v3