Fix deadlocks and races in multi-threaded asyncio logic

[tsmith023]

This PR fixes a host of multi-threading event loop problems by simplifying the logic around creating new event loops and spawning them in threads. Now, the batching code handles its own internal event loop outside of any main thread loop and does so entirely within the context of the background batching thread

[codecov-commenter]

Codecov Report

Attention: 259 lines in your changes are missing coverage. Please review.

Comparison is base (a26557b) 89.38% compared to head (8bc470a) 89.18%.
Report is 228 commits behind head on beta/v4.0.

Files	Patch %	Lines
integration/test_collection_openai.py	33.33%	38 Missing ⚠️
weaviate/collections/batch/base.py	82.43%	26 Missing ⚠️
weaviate/collections/filters.py	73.01%	17 Missing ⚠️
weaviate/collections/data.py	78.57%	15 Missing ⚠️
integration/test_collection_rerank.py	26.31%	14 Missing ⚠️
weaviate/collections/batch/batch_wrapper.py	82.27%	14 Missing ⚠️
weaviate/collections/batch/grpc_batch_objects.py	84.41%	12 Missing ⚠️
weaviate/collections/config.py	66.66%	10 Missing ⚠️
weaviate/client.py	84.48%	9 Missing ⚠️
integration/test_collection_batch_delete.py	94.96%	8 Missing ⚠️
... and 32 more

Additional details and impacted files

@@              Coverage Diff              @@
##           beta/v4.0     #747      +/-   ##
=============================================
- Coverage      89.38%   89.18%   -0.20%     
=============================================
  Files            154      177      +23     
  Lines          16747    18029    +1282     
=============================================
+ Hits           14970    16080    +1110     
- Misses          1777     1949     +172     

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