OPSIM-1157: Add ObservationsArray - change observations to proper numpy subclass

[yoachim]

Make ObservationArray and ScheduledObservationArray subclasses of numpy arrays. Also dropping JSON_Block from the schema.

Quick test shows there's no performance hit making the change. Previous convienince functions updated to be backwards compatible and throw a warning.

[codecov]

Codecov Report

Attention: Patch coverage is 84.09091% with 14 lines in your changes missing coverage. Please review.

Project coverage is 72.85%. Comparing base (bb86895) to head (d15c6c5).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
rubin_scheduler/scheduler/utils/utils.py	72.22%	5 Missing ⚠️
rubin_scheduler/scheduler/surveys/dd_surveys.py	33.33%	2 Missing ⚠️
tests/scheduler/test_example.py	90.00%	1 Missing and 1 partial ⚠️
rubin_scheduler/scheduler/features/features.py	50.00%	1 Missing ⚠️
rubin_scheduler/scheduler/sim_runner.py	66.66%	1 Missing ⚠️
rubin_scheduler/scheduler/surveys/base_survey.py	0.00%	1 Missing ⚠️
rubin_scheduler/scheduler/surveys/desc_ddf.py	50.00%	1 Missing ⚠️
...cheduler/scheduler/surveys/too_scripted_surveys.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
- Coverage   72.87%   72.85%   -0.03%     
==========================================
  Files         143      144       +1     
  Lines       15084    15098      +14     
  Branches     2062     2063       +1     
==========================================
+ Hits        10993    10999       +6     
- Misses       3639     3645       +6     
- Partials      452      454       +2     

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[rhiannonlynne]

Looks good!