Chore: refactor InvarFitting #5206

Job	Run time
Build source distribution	20s
determine-arm64-runner	1s
Build wheels for cp311-manylinux_x86_64	5m 27s
Build wheels for cp311-manylinux_x86_64	5m 28s
Build wheels for cp311-macosx_x86_64	5m 31s
Build wheels for cp311-macosx_arm64	3m 13s
Build wheels for cp311-win_amd64	7m 59s
Build wheels for cp310-manylinux_aarch64	4m 24s
build_pypi_index	10s
build_docker (12)	4m 54s
build_docker (_cu11, 11)	4m 27s
upload_pypi	0s
deploy_pypi_index	0s
Pass testing build wheels	4s
	41m 58s

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