Improved dataset loading; fixes, safeties, diagnostics, and better feedback

[jshook]

This fixes a regression in hdf5 data loading, but it also adds minor improvements for testing diagnostics.
Each functional change is shown on a themed commit, for easier review.

Changes:

1. Fix off-by-one name extraction for .hdf5 dataset names.
2. Add pom config to allow in-process jvm debugging of exec (exec:java).
3. Add missing goal qualifiers to pom entries for exec, to allow IntelliJ to correctly map them.
4. Add logging to dataset loader paths.
5. Make argv to regex processing more defensive.
6. Add warnings to users for invalid dataset name.
7. Make hdf5 loader handle paths correctly.
8. Remove invalid thrown exception in Optional code path.
9. Add example config for yaml-based glove-25-angular, for testing/demonstration purposes.

[github-actions]

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If you did not complete any of these, then please explain below.

[MarkWolters]

LGTM

[tlwillke]

The fix works. The dataset loader is repeating the load 3 times, twice locally cached. This was not introduced by your PR, but can you please attempt a fix while you're at it?

[jshook]

The fix works. The dataset loader is repeating the load 3 times, twice locally cached. This was not introduced by your PR, but can you please attempt a fix while you're at it?

Yes, I'll take a look. I think this is due to no clear distinction between acquiring (a handle to) and accessing (the data therein). I'll see if there is a way to improve it which isn't onerous.

[tlwillke]

The fix works. The dataset loader is repeating the load 3 times, twice locally cached. This was not introduced by your PR, but can you please attempt a fix while you're at it?

Please disregard. It's actually the 3 required files per dataset. No fix required.

[tlwillke]

LGTM