feat: allow single file to be used instead of directory

[tylerriccio33]

PR Checklist

• A description of the changes is added to the description of this PR.
• [] If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added or modified a feature, documentation in docs is updated

Description of changes

This PR allows a single file to be passed to deptry for analysis. I often find myself creating projects with a single file, and would love to use deptry to root out unused dependencies. I couldn't find a way to allow just a single file so I wrote this PR.

The changes are fairly straightforward, I intercept the single file at the rust level in src/python_file_finder.rs. This could easily be done in python but I'd imagine the authors prefer a unified interface.

Let me know what you think!

P.S. Initially marking this as draft since I had some OS related issues running functional tests. My M1 chip can be dicey...

Old Behavior:

New Behavior:

[tylerriccio33]

Anything I can do to push this along?

[fpgmaas]

I am not quite sure yet if this is useful enough for it to be merged to main. Can you elaborate why simply running uv run deptry . would not suffice? If it is a single file, deptry would simply return a list of only that file while scanning for files, and then analyze that, right?

[tylerriccio33]

Occasionally I have other files commingled with the 'main' file. For example, I may have some builder scripts that construct metadata during the package build, but isn't actually required by the 'main' file. Sometimes I'll have a single 'main' file and a single test script. In those 2 cases I will import dev or build dependencies that aren't declared in the pyproject.toml file.

As I say this out loud, maybe there's room to instead, discriminate between regular and dev deps?