Adds vSHARP model and code quality changes

[georgeyiasemis]

• vSHARP Model: Supporting both 2D and 3D. (Details: vSHARP Paper)
• 3D Reconstruction Experiments: Various additions, such as transforms, engine changes (e.g., visualization), and the addition of new metrics and losses used in the vSHARP paper.
• Project Organization: Introduces new project folders for vSHARP and the CMRxRecon challenge.
• Minor Code Quality Enhancements (e.g. Enum capitalization)
• README update

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 89.29032% with 83 lines in your changes are missing coverage. Please review.

Project coverage is 84.49%. Comparing base (b56a724) to head (dcdd5c3). Report is 1 commits behind head on main.

:exclamation: Current head dcdd5c3 differs from pull request most recent head dc69971. Consider uploading reports for the commit dc69971 to get more accurate results

Files	Patch %	Lines
direct/nn/mri_models.py	81.55%	19 Missing :warning:
direct/data/mri_transforms.py	85.34%	17 Missing :warning:
direct/functionals/hfen.py	81.08%	14 Missing :warning:
direct/engine.py	25.00%	12 Missing :warning:
direct/nn/vsharp/vsharp.py	92.40%	12 Missing :warning:
direct/functionals/snr.py	87.50%	3 Missing :warning:
direct/nn/unet/unet_3d.py	98.34%	2 Missing :warning:
direct/nn/vsharp/vsharp_engine.py	96.92%	2 Missing :warning:
direct/predict.py	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #258 +/- ## ========================================== + Coverage 84.05% 84.49% +0.43% ========================================== Files 93 96 +3 Lines 6486 6964 +478 ========================================== + Hits 5452 5884 +432 - Misses 1034 1080 +46 ```

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