Small I/O fixes

[dalmijn]

Issue addressed

Fixes number of smaller I/O issues Fixes #276

Explanation

Bit and pieces of code.

Checklist

• [x] Updated tests or added new tests
• [x] Branch is up to date with main
• [x] Tests & pre-commit hooks pass
• [x] Updated documentation if needed

Additional Notes (optional)

No.

[hboisgon]

I directly changed the PR @dalmijn, hope it's okay. I added some extra things:

• We did not decide but I decide to support the dir_input for staticgeoms. I know already several users that use that option to avoid having too many toml files in their root folder especially for calibration so I think this would be the more robust method.
• For write, I kept your new functionality that filenames can be edited there, I added the states one for completion.
• Added changelog

All the rest was good, thanks for the changes! If you agree with my last modifications, then we can merge :)

Note, I edited the test on ksathorfrac as nowadays read/write netdcf files can be unstable and cause test to hang. The values are different but this is because as we do not write, the catchment mask is not yet applied.

[dalmijn]

@hboisgon, Ill go over it one last time, but it looks good! Thanks for adding to the PR!