Use `ffizz` to build taskchampion-lib

[djmitche]

• https://docs.rs/ffizz-header/latest/ffizz_header/ to generate taskchampion.h
• https://docs.rs/ffizz-string/latest/ffizz_string/ to replace TCString
• https://docs.rs/ffizz-passby/latest/ffizz_passby/ to handle data types other than string

Also, let's rename the C types from things like TCString, TCTask, etc. to tc_string_t, tc_task_t, etc., as that will make room for C++ wrappers with names like TCString, TCTask, etc. in Taskwarrior.

[djmitche]

WIP in https://github.com/djmitche/taskwarrior/pull/new/issue3059 (on top of the add-rust branch)

[djmitche]

GothenburgBitFactory/taskwarrior#3114 partially addresses this.

[djmitche]

This isn't required for 3.0

[djmitche]

The FFI story has changed a bit, now. We're still using ffizz-header, but I don't think using ffizz-string et al. is a good idea.