Add support for DSA-4096 keys and signatures.

[ni4]

Description

There are some keys in a wild which use DSA 4096 bits (example: https://bugzilla.mozilla.org/show_bug.cgi?id=1903976), and those are supported/validated correctly by GnuPG.
We should consider supporting them as well, as currently we limit Q parameter size to 256 bits, while DSA 4096 would need 384.