Better support of projects that use `uv` + `requirements.in`

[fpgmaas]

uv is getting a lot of attention, and seems to be quite popular. It has a similar feature as pip-compile, where it generates a requirements.txt file with all direct and transitive dependencies locked to a specific version. Both uv and pip-compile suggest storing the list of direct dependencies in a requirements.in file.

In projects like this, the default deptry . command will raise likely many incorrect errors: It will point out that many of the dependencies listed in requirements.txt are unused. In these projects, users can configure deptry to work correctly as follows:

deptry --requirements-txt requirements.in .

This is a bit confusing. I suggest we make the following change to improve support of these projects:

1. Renaming the arguments requirements-txt and requirements-txt-dev to requirements-file and requirements-file-dev respectively.

Additionally, this change would also be great for these kind of projects:

2. Checking if both a requirements.in and a requirements.txt file are present in the project. If so, use the requirements.in file.

However (2) is a bit more complicated, I don't see a clean solution for this directly. Currently we allow a user to pass multiple requirement files, and then requirements are read from all specified files. This would somehow need a feature where by default a list is provided (requirements.in, requirements.txt), and only the first one that exists is used. This requires some more thought.