Workflow efficiency improvements: (#44)

* Run build_wheels workflow only when relevant files change.
* Cancel in-progress jobs when a new commit is pushed to the same branch.

.github/workflows/build_wheels.yml

@@ -1,6 +1,41 @@
 name: Build
 
-on: [push, pull_request]
+on:
+  pull_request:
+    paths:
+      - ".clang-format"
+      - ".clang-tidy"
+      - ".github/workflows/build_wheels.yml"
+      - ".gitmodules"
+      - "clp_ffi_py/**"
+      - "MANIFEST.in"
+      - "pyproject.toml"
+      - "README.md"
+      - "requirements-dev.txt"
+      - "setup.cfg"
+      - "setup.py"
+      - "src/**"
+      - "tests/**"
+  push:
+    paths:
+      - ".clang-format"
+      - ".clang-tidy"
+      - ".github/workflows/build_wheels.yml"
+      - ".gitmodules"
+      - "clp_ffi_py/**"
+      - "MANIFEST.in"
+      - "pyproject.toml"
+      - "README.md"
+      - "requirements-dev.txt"
+      - "setup.cfg"
+      - "setup.py"
+      - "src/**"
+      - "tests/**"
+
+concurrency:
+  group: "${{github.workflow}}-${{github.ref}}"
+  # Cancel in-progress jobs for efficiency
+  cancel-in-progress: true
 
 jobs:
   linters: