ci: add paths filter to pull_request test trigger

only run tests when relevant files change (src/, tests/, uv.lock, pyproject.toml, .github/workflows/)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/run-tests.yml

@@ -14,8 +14,13 @@ on:
       - "pyproject.toml"
       - ".github/workflows/**"
 
-  # run on all pull requests because these checks are required and will block merges otherwise
   pull_request:
+    paths:
+      - "src/**"
+      - "tests/**"
+      - "uv.lock"
+      - "pyproject.toml"
+      - ".github/workflows/**"
 
   workflow_dispatch: