Enable cache, swap to pyproject.toml for python version control

.github/workflows/test.yaml

@@ -8,5 +8,6 @@ jobs:
     - uses: actions/checkout@v4
     - uses: astral-sh/setup-uv@v6
       with:
-        python-version: '3.13'
+        enable-cache: true
+        python-version-file: pyproject.toml
     - run: uv run --frozen black --check src/

pyproject.toml

@@ -1,7 +1,8 @@
 [project]
 name = "feedsummarizer"
 version = "0.1.0"
-requires-python = ">=3.11"
+# Pinned to 3.13 so we stay in line with AWS' Lambda runtime
+requires-python = "3.13"
 dependencies = []
 
 [dependency-groups]