Cleanup

Nobody has claimed this yet.

The goal of this issue is to track progress of some general cleanup efforts related to the package.

We recently did some bigger changes to the package which have not yet fully propagated to all docs/tutorials/examples. This is mostly the case for the new transforms which replace the `ImageCollateFunction` in #1074.

But the package also accumulated many smaller inconsistencies over the years,

**Main Goals**
* Update docs: Use transforms instead of `ImageCollateFunction`
* Cleanup tests: All tests should be written in pytest format
* Cleanup docstrings: Add missing or update docstrings and make formatting consistent

As always, any contributions/feedback is very welcome!

## Tasks

- [ ] #1204
- [ ] #1206
- [ ] #1216
- [x] #1228
- [ ] #1229
- [x] #1227
- [x] #1184
- [x] #1182
- [x] #1200
- [x] #1201
- [x] #1202
- [x] #1203
- [x] #1214
- [x] #1215
- [x] #1225
- [x] #1226
- [x] #1375
- [x] #1376

Start by reviewing the unchecked task issues #1204, #1206, #1216, and #1229, then inspect the docs, tutorials, examples, tests, and docstrings affected by the cleanup. Done means completing one clearly scoped task, including the requested transform, pytest, or documentation consistency updates.

Written by the indexing model from the issue text.