Pickle instead of scatter.

[delucchi-cmu]

Change Description

Closes #302.

Writes the file reader to a pickled file, and de-pickles in the mapping and splitting workers.

Writes the alignment to a pickled file, and de-pickles in the splitting workers. destination map is created on-demand, and is owned by the resume plan, as this is used to determine remaining reduce tasks.

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

[codecov[bot]]

Codecov Report

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

Project coverage is 99.78%. Comparing base (c5e6095) to head (a66e111).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #328 +/- ## ========================================== + Coverage 99.56% 99.78% +0.21% ========================================== Files 26 26 Lines 1379 1389 +10 ========================================== + Hits 1373 1386 +13 + Misses 6 3 -3 ```

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