fix: add missing f-string prefix for --parallel bootstrap arg (#665)

The --parallel={parallel} argument was a regular string instead of an
f-string, causing it to literally pass "--parallel={parallel}" to the
cmake bootstrap script instead of the actual parallel job count.

This resulted in single-threaded bootstrap compilation regardless of
CMAKE_BUILD_PARALLEL_LEVEL setting.

Author: shanemcd

_build_backend/backend.py

@@ -120,7 +120,7 @@ def _bootstrap_build(temp_path: str, config_settings: dict[str, list[str] | str]
         bootstrap_path = next(temp_path_.glob("cmake-*/bootstrap"))
         prefix_path = temp_path_ / "cmake-install"
         cmake_path = prefix_path / "bin" / "cmake"
-        bootstrap_args = [f"--prefix={prefix_path}", "--no-qt-gui", "--no-debugger", "--parallel={parallel}", "--", "-DBUILD_TESTING=OFF", "-DBUILD_CursesDialog:BOOL=OFF"]
+        bootstrap_args = [f"--prefix={prefix_path}", "--no-qt-gui", "--no-debugger", f"--parallel={parallel}", "--", "-DBUILD_TESTING=OFF", "-DBUILD_CursesDialog:BOOL=OFF"]
         previous_cwd = Path().absolute()
         os.chdir(bootstrap_path.parent)
         try: