add tests for summary networks [WIP]

[rusty-electron]

I will be adding more commits to this PR as per instructions from @LarsKue.

Updates to test fixtures:

• tests/conftest.py: Modified the summary_network fixture to accept the summary_dim parameter.
• tests/test_networks/conftest.py: Added new fixtures for summary_dim, key_dim, and various network instances (lst_net, set_transformer, set_transformer_key_dim_variation, deep_set).

New test cases:

• tests/test_networks/test_summary_networks.py: Introduced new test cases test_compute_metrics and test_set_transformer_with_key_dim to verify the functionality of the new attributes and ensure the correctness of the network outputs.

[LarsKue]

Thank you for the PR. Please make sure that the linter passes before merging.

[paul-buerkner]

In an attempt to merge this PR, I noticed that there are some unknown arguments used in set_transformer, namely key_dim and num_attention_blocks.

@LarsKue I think you will need to check and fix this before you can merge it as I don't understand the context in which these changes were made.

[LarsKue]

@paul-buerkner please never merge PRs that do not at the very least pass all tests, unless you have very good reason to. I will look into this as soon as I have a time slot available.

[paul-buerkner]

I did not intend to merge this PR without consultation (even if all tests would have passed, which they are not because of the issue I brought up). I just wanted to move it forward. My earlier message was unclear in this regard. Sorry for that.