applet.interface.uart: add commentary about the autobaud and its limitations

software: depend on amaranth-yosys directly. Pip seems to backtrack indefinitely with amaranth[builtin-yosys].

software: tighten dependency to aiohttp~=3.8. Fixes #294.

firmware: Add revC3 and support for the new A DAC.

software: Add support for revC3

CI: fix branch name.

firmware: switch the DAC off too when switching off Vio Without this, the DAC still outputs it's control voltage even if Vio is off. This goes through the feedback resistors to the output. I measured about 15 mV without this patch on a port that was previously enabled. With this patch it properly goes down to zero. While such a low voltage usually shouldn't be a problem, I consider it unclean design, especially if it is so easy to fix.

software: migrate from setup.py to pyproject.toml.

software: update uses of deprecated Amaranth APIs.

Update self-build suggestions to refer to revC2.