Tests / fixes for `moveBy`

[haberdashPI]

Adds tests to verify working unit motions, and simplifies and corrects the unit-motion logic.

TODO:

• [x] add tests for multi-line regex unit motions
• [x] remove skiped tests and verify they pass
• [x] add extend by tests for end at end of file and start at start of file
• [x] briefly review narrowTo behavior to verify it is working okay (this PR will not add formal tests, c.f. #44 for narrowBy tracking)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.39252% with 6 lines in your changes missing coverage. Please review.

Project coverage is 42.07%. Comparing base (386a933) to head (571cc99).

Files with missing lines	Patch %	Lines
src/web/unitMotions.ts	96.19%	4 Missing :warning:
src/web/activeMotions.ts	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #52 +/- ## =========================================== + Coverage 25.08% 42.07% +16.99% =========================================== Files 10 10 Lines 925 927 +2 Branches 249 240 -9 =========================================== + Hits 232 390 +158 + Misses 688 535 -153 + Partials 5 2 -3 ```

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