CI: Add workflow to create Advent of Code puzzle issues

CI:
- Add a workflow to create issues for Advent of Code puzzles, including instructions for solution and test file placement, and a comment requesting automated analysis from Sourcery.

Resolves #3

.github/workflows/create-puzzle-issue.yml

@@ -0,0 +1,40 @@
+name: Create Puzzle Issue
+
+on:
+  workflow_call:
+    inputs:
+      year:
+        required: true
+        type: number
+        description: "The year of the puzzle"
+      day:
+        required: true
+        type: number
+        description: "The day of the puzzle"
+      part:
+        required: true
+        type: number
+        description: "The part of the puzzle (1 or 2)"
+
+permissions:
+  issues: write
+
+jobs:
+  create-issue:
+    runs-on: ubuntu-latest
+    env:
+      GH_TOKEN: ${{ secrets.USER_TOKEN }}
+    steps:
+      - name: Create puzzle issue
+        id: create-issue
+        run: |
+          ISSUE_URL=$(gh issue create \
+            --title "Advent of code - ${{ inputs.year }} day ${{ inputs.day }} part ${{ inputs.part }}" \
+            --body "Write solution in \`puzzles/year_${{ inputs.year }}/day_${{ inputs.day }}/solution.py\`, and write tests in \`puzzles/year_${{ inputs.year }}/day_${{ inputs.day }}/test_solution.py\` using relative imports")
+          echo "issue_url=${ISSUE_URL}" >> $GITHUB_OUTPUT
+
+      - name: Add sourcery comment
+        run: |
+          gh issue comment "${ISSUE_URL}" --body "@sourcery-ai develop - you can read the puzzle statement with \`uv run advent_of_code.py read ${{ inputs.year }} ${{ inputs.day }} ${{ inputs.part }}\`. Run the solution on \`puzzles/year_${{ inputs.year }}/day_${{ inputs.day }}/input.txt\` and write answer to \`puzzles/year_${{ inputs.year }}/day_${{ inputs.day }}/answer_part${{ inputs.part }}.txt\`"
+        env:
+          ISSUE_URL: ${{ steps.create-issue.outputs.issue_url }}