Cut unused variables and fix off-by-one

This release cuts unused variables. It also fixes an off-by-one condition, for counting batch numbers from the high end of sieving intervals. (This is more important to PRIME_PROVER mode than to FACTOR_FINDER, as PRIME_PROVER might actually sieve the entire range, whereas FACTOR_FINDER will reasonably never be expected to do so.)

Full Changelog: v6.4.0...v6.4.1

sha1sum results:
a823e69db4042141f7b480dd5045fb19f9d6d479 FindAFactor-6.4.1-cp310-cp310-manylinux_2_35_x86_64.whl
ac591e9c5d7bf2778c7176141f45e2b9f4a8f591 FindAFactor-6.4.1-cp312-cp312-manylinux_2_39_x86_64.whl
289471ad86a31e3641fceff1009ce9b67f04b273 FindAFactor-6.4.1-cp312-cp312-win_amd64.whl
2d29bf06fc8cf22a72d3c44377e51c5493618cb2 FindAFactor-6.4.1-cp313-cp313-macosx_13_0_x86_64.whl
cda978e5f5b440a762d679bacd38c9968baf3b28 FindAFactor-6.4.1-cp313-cp313-macosx_14_0_arm64.whl
a71ccc428af5a3b04dbfb3110b6167b7fded2925 FindAFactor-6.4.1-cp313-cp313-macosx_15_0_arm64.whl
fde7ada73f168fa7f82506fdfb436cf4b86de9c9 FindAFactor-6.4.1-cp38-cp38-manylinux_2_31_x86_64.whl
887cd49c7e4b83c1979fa1497eef982e75d466c7 findafactor-6.4.1.tar.gz