Chore: refactor InvarFitting #5207

Job	Run time
Build source distribution	20s
determine-arm64-runner	1s
Build wheels for cp311-manylinux_x86_64	5m 31s
Build wheels for cp311-manylinux_x86_64	5m 28s
Build wheels for cp311-macosx_x86_64	6m 16s
Build wheels for cp311-macosx_arm64	3m 1s
Build wheels for cp311-win_amd64	5m 1s
Build wheels for cp310-manylinux_aarch64	4m 30s
build_pypi_index	16s
build_docker (12)	3m 43s
build_docker (_cu11, 11)	4m 1s
upload_pypi	0s
deploy_pypi_index	0s
Pass testing build wheels	8s
	38m 16s

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