thirdparty: vendor tomli...
thirdparty: vendor tomli
The next commit will introduce a .toml file to abstract configitems
away from Python. Python 3.11 has a toml read-only library (`tomllib`), which
gives us a way out of vendoring eventually.
For now, we vendor the backport, specifically version 1.2.3 which is still
compatible with Python 3.6.
