✨♻️ refactor preprocessing

[dyollb]

What do these changes do?

The PR adds

• SelectChannel transform
• an option to crop the foreground using an otsu mask (thresholding the first channel)
• various small fixes
• improve predict command, to write metrics in csv file, plot summary confusion matrix

Related issue/s

How to test

• run pytest

Checklist

• [x] Non-breaking change (fix or new feature that would not break existing functionality).
• [x] Unit tests for the changes and run locally with the command pytest tests
• [x] Runs on minimum Python version

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.75949% with 62 lines in your changes are missing coverage. Please review.

Project coverage is 56.77%. Comparing base (288663f) to head (dfd3452).

Files	Patch %	Lines
src/segmantic/seg/monai_unet.py	16.07%	45 Missing and 2 partials :warning:
src/segmantic/seg/losses.py	73.17%	5 Missing and 6 partials :warning:
src/segmantic/seg/transforms.py	92.00%	1 Missing and 1 partial :warning:
src/segmantic/seg/visualization.py	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #64 +/- ## ========================================== + Coverage 55.47% 56.77% +1.30% ========================================== Files 21 23 +2 Lines 1325 1409 +84 Branches 237 251 +14 ========================================== + Hits 735 800 +65 - Misses 550 562 +12 - Partials 40 47 +7 ``` | [Flag](https://app.codecov.io/gh/dyollb/segmantic/pull/64/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bryn+Lloyd) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/dyollb/segmantic/pull/64/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bryn+Lloyd) | `56.77% <60.75%> (+1.30%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bryn+Lloyd#carryforward-flags-in-the-pull-request-comment) to find out more.

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