Refactor to separate sync and async connections

[tsmith023]

This PR constitutes a complete overhaul of the codebase structure with respect to the underlying connections of the WeaviateClient and WeaviateAsyncClient classes and how they are provided to them. Currently, the WeaviateClient works by using the same ConnectionV4 (which is async) object under-the-hood that the WeaviateAsyncClient uses only with the calls scheduled in a side-car event loop thread.

With this PR, this is has been refactored so that the connection can be dependency injected into the business logic layer of the client from the top-down so that all namespaces in WeaviateClient now explicitly depend on ConnectionSync, which itself depends on httpx.Client and grpc.Channel, with ConnectionV4 renamed to ConnectionAsync that still depends on httpx.AsyncClient and grpc.aio.Channel.

This is achieved using the command pattern whereby all business logic of the client is encapsulated into Executor classes, e.g. _DataExecutor, which expose methods that exactly match those of the public API plus an additional argument: connection: ConnectionSync | ConnectionAsync. Then, at runtime, the connection is injected into the executor call by the decorator @weaviate.connect.impl.generate("sync" | "async") so that we can have a single implementation of the inner business logic in the executor that is agnostic to exactly which connection is passed to it. The executor methods work with the union of connections by utilising the logic in weaviate/connect/executor.py, which is effectively an ad hoc implementation of callbacks.

This PR introduces the fundamental structure of the overall pattern that the client should use moving forward. However, there is a large amount of boilerplate associated with the stitching together of the sync/async clients with the executors. This should be automated in the future through custom-built auto-generation tools that translate the API surfaces of the executors into the async_.pyi and sync.pyi stub files of each namespace. Until then effort should also be spent developing a custom flake8 linter to validate that the namespace async_.pyi and sync.pyi files are identical.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 86.08113% with 374 lines in your changes missing coverage. Please review.

Project coverage is 87.82%. Comparing base (9ef4682) to head (4ce71b8). Report is 123 commits behind head on main.

Files with missing lines	Patch %	Lines
weaviate/connect/v4.py	78.79%	102 Missing :warning:
weaviate/backup/executor.py	68.91%	60 Missing :warning:
weaviate/connect/authentication.py	86.33%	19 Missing :warning:
weaviate/rbac/executor.py	80.00%	18 Missing :warning:
weaviate/connect/executor.py	80.00%	16 Missing :warning:
weaviate/collections/aggregations/executor.py	38.09%	13 Missing :warning:
weaviate/collections/tenants/executor.py	77.96%	13 Missing :warning:
weaviate/users/executor.py	89.62%	11 Missing :warning:
weaviate/collections/config/executor.py	91.86%	10 Missing :warning:
...lections/queries/fetch_objects_by_ids/executors.py	70.58%	10 Missing :warning:
... and 28 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1594      +/-   ##
==========================================
- Coverage   88.39%   87.82%   -0.57%     
==========================================
  Files         187      219      +32     
  Lines       16015    17492    +1477     
==========================================
+ Hits        14156    15362    +1206     
- Misses       1859     2130     +271     

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[eavanvalkenburg]

This change broke unit tests for me, because suddenly the create and other method on this AsyncMock(spec=_CollectionsAsync) are created as MagicMock, rather then AsyncMock...

[tsmith023]

Hi @eavanvalkenburg, thanks for raising! I'll look into how we can work around that and release a fix

[eavanvalkenburg]

was able to work around it, by doing this:

# previous code:
async_mock = AsyncMock(spec=WeaviateAsyncClient)
async_mock.collections = AsyncMock(spec=_CollectionsAsync)
# new additions:
async_mock.collections.create = AsyncMock()
async_mock.collections.delete = AsyncMock()
async_mock.collections.exists = AsyncMock()