Skip .venv and .git when searching workspace

[bluss]

Skip .venv since it can contain stray pyprojects that are not related to
the current project. Further items could be ignored here.

Correctness fix (previously pyproject.toml installed into some package
in the environment, could ruin the sync), as well as a speed up since we
can skip scanning all the files in the environment.

Also change the order of member check and loading the project, it
seemed better to me in this order.

Fixes #260

[bluss]

Can ignore other files. Could ignore all with "." prefix for example.

The second commit can be dropped if there is some reason it's not the right change. It just seems a bit wrong to parse a file that we aren't even asked to read (because it's not in the workspace.)

[mitsuhiko]

I think this is good. Thanks. Longer term it might make sense to investigate the ignore crate but maybe it's weird to magically ignore everything ignored by .gititnore.

[bluss]

Thanks for the nice work on rye.

For fun, maybe skipping .git seems weird. But just "git tag pyproject.toml" in a workspace and we would get (in rye 0.4.0):

    0: failed to parse pyproject.toml from [snip...]/.git/refs/tags/pyproject.toml in context of workspace [...]:
    1: TOML parse error at line 1, column 41
         |
       1 | 600a531ad4e481076ef62c3fb83505f57191e3c3
         |                                         ^
       expected `.`, `=`

[mitsuhiko]

No I agree that .git should be skipped. Maybe the non confusing thing would be to really skip anything with a leading .. I don't see that much harm in it. However the reason I thought ignore might be reasonable is that people might have node_modules and god knows what kind of nonsense is in there.