Add setting of number_extended_events

[mwregan2]

Related to JP-3096

This PR fixes the population of the new EXTNCRS keyword, which was not being set when in single processing mode.

Checklist

• [x] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [x] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [x] added relevant label(s)

[codecov[bot]]

Codecov Report

Patch coverage: 22.22% and project coverage change: -0.06 :warning:

Comparison is base (e0c6f69) 74.46% compared to head (eb5255d) 74.41%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #178 +/- ## ========================================== - Coverage 74.46% 74.41% -0.06% ========================================== Files 29 29 Lines 5937 5944 +7 ========================================== + Hits 4421 4423 +2 - Misses 1516 1521 +5 ``` | [Impacted Files](https://app.codecov.io/gh/spacetelescope/stcal/pull/178?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | Coverage Δ | | |---|---|---| | [src/stcal/jump/jump.py](https://app.codecov.io/gh/spacetelescope/stcal/pull/178?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-c3JjL3N0Y2FsL2p1bXAvanVtcC5weQ==) | `62.92% <0.00%> (-0.87%)` | :arrow_down: | | [tests/test\_jump.py](https://app.codecov.io/gh/spacetelescope/stcal/pull/178?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope#diff-dGVzdHMvdGVzdF9qdW1wLnB5) | `88.46% <50.00%> (-0.32%)` | :arrow_down: |

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[hbushouse]

Don't understand why the one pytest that was unskipped is causing failures in the CI tests (claims it can't find the input data file, which is clearly present in the data directory), but runs fine when I test it locally. So just to get the CI tests to work I marked it to be skipped again.

[hbushouse]

@ddavis-stsci Can you please review for Roman?

[hbushouse]

OK, it looks like we're all in agreement. Merging now.