add md6 modes

[cyclone-github]

Add modes:

md6-128
md6-224
md6-256
md6-384
md6-512

[cyclone-github]

MD6-* Benchmarks:

$ hashgen -w /media/ramdisk/rockyou.txt -b -m md6-128
2026/04/13 14:50:57 Finished processing 14344391 lines in 3.516 sec (4.080 M lines/sec)

$ hashgen -w /media/ramdisk/rockyou.txt -b -m md6-224
2026/04/13 14:51:11 Finished processing 14344391 lines in 4.654 sec (3.082 M lines/sec)

$ hashgen -w /media/ramdisk/rockyou.txt -b -m md6-256
2026/04/13 14:51:20 Finished processing 14344391 lines in 4.928 sec (2.911 M lines/sec)

$ hashgen -w /media/ramdisk/rockyou.txt -b -m md6-384
2026/04/13 14:51:37 Finished processing 14344391 lines in 6.444 sec (2.226 M lines/sec)

$ hashgen -w /media/ramdisk/rockyou.txt -b -m md6-512
2026/04/13 14:51:49 Finished processing 14344391 lines in 7.705 sec (1.862 M lines/sec)