Fix FACTOR_FINDER node bounds

This release correctly divides node work segments for FACTOR_FINDER mode. (We already figured this out for PRIME_PROVER, but the developer was simply sloppy about applying the lesson, previously.)

Full Changelog: v6.2.0...v6.2.1

sha1sum results:
6e49a98b914c94ffb267fbde7c2f171505e06832 FindAFactor-6.2.1-cp310-cp310-manylinux_2_35_x86_64.whl
e2bb102ed0f4e7958499705acf78ee9dc68a5205 FindAFactor-6.2.1-cp312-cp312-manylinux_2_39_x86_64.whl
aa5496f394965f3380b9e45a54cced79dda3112b FindAFactor-6.2.1-cp312-cp312-win_amd64.whl
669bc482c27248adc43992864df0517f80c759fb FindAFactor-6.2.1-cp313-cp313-macosx_13_0_x86_64.whl
42634af348897e0fc720e1b3961ad64efb265836 FindAFactor-6.2.1-cp313-cp313-macosx_14_0_arm64.whl
3bf59decaf00dd2ae765c0daad7026053e08b8ef FindAFactor-6.2.1-cp313-cp313-macosx_15_0_arm64.whl
6f32205e5360615f174fddb9660f5100d5b9bde1 FindAFactor-6.2.1-cp38-cp38-manylinux_2_31_x86_64.whl
596fd74f151ad065a82c7a8a9c4f2032fcbfc283 findafactor-6.2.1.tar.gz