[ENH]added multiloss support for v2 interface of base model class

[Soham-47]

Added MultiLoss support for to_prediction and to_quantiles methods of base model v2 class

[codecov]

Codecov Report

❌ Patch coverage is 48.48485% with 17 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@cf46d07). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pytorch_forecasting/models/base/_base_model_v2.py	42.85%	16 Missing ⚠️
...orch_forecasting/models/samformer/_samformer_v2.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2122   +/-   ##
=======================================
  Coverage        ?   86.52%           
=======================================
  Files           ?      165           
  Lines           ?     9753           
  Branches        ?        0           
=======================================
  Hits            ?     8439           
  Misses          ?     1314           
  Partials        ?        0           

Flag	Coverage Δ
cpu	86.52% <48.48%> (?)
pytest	86.52% <48.48%> (?)

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[PranavBhatP]

Hi, if the PR is still not ready for review, you can revert to a draft PR, I don't see any reviewable code right now.