feat: extend EpochMetric to support more compute_fn output types

[zongyang078]

Fixes #1757

Description:
Extends EpochMetric to support more output types returned by compute_fn, as requested in #1757.

Previously, compute_fn could only return scalar values (int/float). This PR adds support for:

• torch.Tensor
• tuple / list of tensors
• Mapping (e.g. dict) of tensors

A TypeError with a clear message is raised for unsupported output types. The existing apply_to_type utility is reused for distributed broadcasting of non-scalar results.

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[aaishwarymishra]

Just to be sure we also should check if the output values are as expected or correct after the computation.

[zongyang078]

Added value verification for all output types — each test now checks that the result matches directly calling compute_fn on the concatenated data.

[Abhisri436]

Hi! I’m working on issue #1757 for a course contribution and noticed this PR already covers the main source changes.

I added value-checking tests on my fork for scalar tensor, vector tensor, tuple/list of tensors, and mapping outputs. These tests check the actual computed values, which seems related to the review comment about verifying output correctness.

Test commit: Abhisri436@56345826

Would it be useful for me to adapt these tests into this PR or keep them as a separate reference?

[aaishwarymishra]

@Abhisri436 It's generally not a good Idea to implement the changes as an external pr until explicitly mentioned that the change if a future improvement or can be done separately :)