Add Deptry, split dev into dev and docs recipes, address bandit security issues

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• Tests for the changes have been added (for bug fixes / features)
  • (If applicable) Documentation has been added / updated (for bug fixes / features)
• CHANGES.rst has been updated (with summary of main changes)
  • Link to issue (:issue:number) and pull request (:pull:number) has been added

What kind of change does this PR introduce?

• Adds the deptry package to the linters for performing dependency analyses (unused or missing)
• Pinned a few linting dependencies
• Splits the dev dependencies into dev and docs (both can be installed with all)
• Enables flake8-bandit like checks in ruff, fixes a few security-related checks
• xclim.testing.utils now have more secure URL auditing checks

Does this PR introduce a breaking change?

Yes, a new dependency has been added (deptry).

Also, xclim no longer bundles the documentation dependencies with the dev recipe. Splitting this reduces the number of dependencies needed to run the tests and also helps us know which dependencies are needed and where (determined with the aid of deptry).

Other information:

https://deptry.com/
https://docs.astral.sh/ruff/rules/#flake8-bandit-s

[aulemahal]

The meta changes look good, as far as I understand, thanks!

However, I think the change in convert_units_to is to strict. It would yield incomprehensible error messages to the user.

[aulemahal]

A suggestion to make the error message even more explicit, but otherwise, this is good to go!

[coveralls]

coverage: 90.649% (+0.05%) from 90.595%
when pulling 8c83c69 on deptry
into a375d78 on main.

[coveralls]

coverage: 90.639% (+0.04%) from 90.595%
when pulling 59fa5c1 on deptry
into a375d78 on main.

[coveralls]

coverage: 90.649% (+0.05%) from 90.595%
when pulling a2d84f1 on deptry
into e8d2f36 on main.

[coveralls]

coverage: 90.649% (+0.05%) from 90.595%
when pulling 87f35da on deptry
into 23fd681 on main.