Implemented `training_step` and `validation_step`, fixed all the configs needed to instantiate the lightning module

Description

This PR finally implements a working training loop for the lightining module VAEModule.

What: we added training_step and validation_step plus all the required methods. We also fixed some bugs in the configs (pydantic model) describing the different model components.
Why: To be able to train a LVAE model.
How: see below.

Changes Made

Added:
- training_step and validation_step in the lightning VAEModule (plus other related methods).
- Some required attributes and validators in the VAEAlgorithmmConfig.
- An example notebook to illustrate how to train the LVAE model using current lightning API.
- RunningPSNR class in metrics.py.
- Tests for the added features.
Modified:
- Typing and validators in different pydantic models (e.g., lvae_model.py, nm_model.py)
Removed: Nothing in particular.

Things that can be improved

validation_step requires some additional methods for computing the PSNR at each epoch. These methods are currently within the VAEModule since require some of its attributes. If possible, it would be nice to move this methods out of the lightning module to have something cleaner.

Please ensure your PR meets the following requirements:

[x] Code builds and passes tests locally, including doctests
[x] New tests have been added (for bug fixes/features)
[x] Pre-commit passes
[ ] PR to the documentation exists (for bug fixes / features)

Codecov Report

Attention: Patch coverage is 94.39252% with 6 lines in your changes missing coverage. Please review.

Project coverage is 87.20%. Comparing base (692429e) to head (35c2901). Report is 1 commits behind head on main.

Files	Patch %	Lines
src/careamics/lightning/lightning_module.py	93.33%	3 Missing :warning:
src/careamics/models/lvae/noise_models.py	62.50%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #218 +/- ## ========================================== + Coverage 85.80% 87.20% +1.39% ========================================== Files 130 130 Lines 4799 4876 +77 ========================================== + Hits 4118 4252 +134 + Misses 681 624 -57 ```

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CAREamics / careamics