feat: Points plan selector

[tlambert03]

this pulls out the left half of the FOV selector into a useq widget whose value is one of a number of relative point plans. Next step is to put it back into a joint widget with the view on the right side, connect it's valueChanged to update the view

(this is modified from @fdrgsp's code in #308 and he is marked as author in the git history)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.02326% with 6 lines in your changes missing coverage. Please review.

Project coverage is 90.06%. Comparing base (f04ac7e) to head (2c33634). Report is 32 commits behind head on main.

Files with missing lines	Patch %	Lines
...useq_widgets/points_plans/_points_plan_selector.py	92.59%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #315 +/- ## ========================================== + Coverage 90.03% 90.06% +0.02% ========================================== Files 70 71 +1 Lines 7837 7919 +82 ========================================== + Hits 7056 7132 +76 - Misses 781 787 +6 ```

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[fdrgsp]

@tlambert03 can we make the single FOV text bold and centered as random points and grid? and Is it ok to have all of them in a QGroupBox?

[tlambert03]

yep!

[tlambert03]

just a moment

[tlambert03]

all set

[fdrgsp]

@tlambert03 ready to merge?

[tlambert03]

yep!