Give a UserWarning when Parameter is overriden by name

[edrogers]

This adds a UserWarning when two parameters on one command have a name conflict. Very interested in thoughts and feedback.

• fixes Issue UserWarning when overriding Parameter name #2396

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[emlowe]

This issue recently caused Chia a little grief when a short name collision was merged in - so I'm in support of this concept.

[AndreasBackx]

The implementation proposed here checks every single time an option is used, whether its name has been used before. I moved this check to Command.get_params so it only does this check once on command execution. The downside is that this will only be shown when the command is run, though this seems like a valid trade-off.

Additionally, the error message does not tell you which parameters. That could technically be done, but I'm not sure it's worth the extra time spent as it should be relatively straightforward to figure out.