Add NNX/Linen API consistency test for Conv layer

[Micky774]

What does this PR do?

Added NNX/Linen API consistency test for Linear/Dense layer

Checklist

• This PR fixes a minor issue (e.g.: typo or small bug) or improves the docs (you can dismiss the other
  checks if that's the case).
• This change is discussed in a Github issue/
  discussion (please add a
  link).
• The documentation and docstrings adhere to the
  documentation guidelines.
• This change includes necessary high-coverage tests.
  (No quality testing = no merge!)

[Micky774]

@cgarciae note that this new test alone takes about 45s on my machine (w/ GPU) to run. It covers all the commonly used, public API but is pretty slow. Let me know if you think we need to tweak the coverage.