[BUG] Inconsistent pipeline design and missing return type hints in dataset loaders

[TrishaG189]

Reference Issues/PRs

Closes #406

---

What does this implement/fix? Explain your changes.

While going through the code, I noticed a small inconsistency in how pipelines are implemented:

• AptaNetPipeline follows the sklearn interface (BaseEstimator)
• AptaTransPipeline is implemented as a regular class

I haven’t changed the pipeline behavior here, but wanted to highlight this inconsistency as part of the fix.

Along with that, I added missing return type hints to dataset loaders:

• load_1brq
• load_1gnh

These changes make the code a bit easier to understand and improve IDE support.

---

What should a reviewer concentrate their feedback on?

• Whether aligning pipeline interfaces (AptaTrans vs AptaNet) is something worth standardizing
• If the return type hints for loaders look correct

---

Did you add any tests for the change?

No new tests were added since this only involves type hints and minor structural consistency. All existing tests pass.

---

Any other comments?

Happy to take this further (e.g., making AptaTransPipeline sklearn-compatible) if that direction makes sense.

---

PR checklist

• The PR title starts with either [ENH], [MNT], [DOC], or [BUG].
• Added/modified tests
• Used pre-commit hooks when committing to ensure that code is compliant with hooks.