Fail fast on reduce stage failures.

[delucchi-cmu]

Change Description

Closes #300.

Adds code path for the waiting for futures operation to re-raise exception on the first exception encountered. The reducing stage is a little unique, in that a failure in some shard indicates that the whole pipeline may be experiencing issues, whereas failures at mapping and splitting are more likely to indicate a problem with an individual file.

Code Quality

• [x] I have read the Contribution Guide and LINCC Frameworks Code of Conduct
• [x] My code follows the code style of this project
• [x] My code builds (or compiles) cleanly without any errors or warnings
• [x] My code contains relevant comments and necessary documentation

Project-Specific Pull Request Checklists

New Feature Checklist

• [x] I have added or updated the docstrings associated with my feature using the NumPy docstring format
• [ ] I have updated the tutorial to highlight my new feature (if appropriate)
• [ ] I have added unit/End-to-End (E2E) test cases to cover my new feature
• [ ] My change includes a breaking change
  • [ ] My change includes backwards compatibility and deprecation warnings (if possible)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.52%. Comparing base (37ce248) to head (63e8684).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #317 +/- ## ======================================= Coverage 99.52% 99.52% ======================================= Files 25 25 Lines 1270 1272 +2 ======================================= + Hits 1264 1266 +2 Misses 6 6 ```

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