perf(build): parallelize cython extension compilation (#230)

Author: bdraco

build_ext.py

@@ -45,6 +45,8 @@
 
 class BuildExt(build_ext):
     def build_extensions(self) -> None:
+        if self.parallel is None:  # type: ignore[has-type, unused-ignore]
+            self.parallel = os.cpu_count() or 1
         try:
             super().build_extensions()
         except Exception:  # noqa: S110