make base frame signature match subclasses

[alexrudd2]

Simple method call signature cleanup.

Currently FramerBase and FramerAscii use the parameter data: bytes, and the others use pdu: bytes. pdu is more descriptive.

[janiversen]

Good catch, THANKS.

[alexrudd2]

Credit to pyright here; it catches different things than mypy. But there are ~40 errors remaining with the default settings, and some of them are false positives.