Add a second variant of MNIST CNN

[sgligorijevicTT]

Ticket

This addresses a part of #203
Also fixes #204

Problem description

We want to test more variations of CNNs

What's changed

I refactored the folder structure of the tests and added a new test

Checklist

• New/Existing tests provide coverage for changes

[github-actions]

	Tests	Passed ✅	Skipped ⚠️	Failed
TT-XLA Tests	451 ran	385 passed	66 skipped	0 failed

Test	Result
No test annotations available

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.03%. Comparing base (c1cb43a) to head (2f4471c).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #207   +/-   ##
=======================================
  Coverage   77.03%   77.03%           
=======================================
  Files          21       21           
  Lines        1006     1006           
=======================================
  Hits          775      775           
  Misses        231      231           

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