chore: pass target file and exclusions out of plugin

[thomasschafer]

• Tests written and linted ℹ︎
• Documentation written ℹ︎ - n/a
• Commit history is tidy ℹ︎

What this does

This PR:

• Passes the target file out of the uv plugin, replacing the hardcoded uv.lock
• Does a little refactoring in preparation for passing excluded files out of the plugin, which will be any pyproject.toml and requirements.txt files in the uv project directory. Unfortunately we are not able to wire this all up yet, which is why a couple of lines are commented out, as the --exclude flag in the CLI only accepts file or directory names (e.g. requirements.txt or dir), and not full paths (e.g. dir/requirements.txt), which is not acceptable to us currently as do not want to add blanket excludes in this way - we need more targeted exclusions. This will be addressed in another story.

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