Move `/src/pyproject.toml` to `/pyproject.toml`

[ahouseholder]

It would be easier to work with uv commands if we didn't have to remember to always specify --project=src when doing any uv foo things. This isn't as big a deal when we're doing things via Dockerfile or Makefile or the like, but it's bitten me a few times when using uv at the command line. I think it's probably pretty straightforward to move ./src/pyproject.toml to ./pyproject.toml then clean up any uv foo --project=src commands and be done with it once and for all. I might be wrong of course, but if we could do this it'd make life a smidge easier for future us.