Removed an unnecessary TODO message and reverted a class name change for BaseHTTPTransport.

GH-4568

Adds test coverage for the error handling path when HTTP requests return
error status codes.

GH-4568

Restore comments accidentally removed during a previous commit.

Refactored class names such that BaseHttpTransport now has the same functionality as before the hierarchy refactor

GH-4568

Add a new flush_async method in the Transport ABC. This is needed for the async transport, as calling it from the client
while preserving execution order in close will require flush to be a coroutine, not a function.

GH-4568

Move flush_async down to the specific async transport subclass. This makes more sense anyway, as
this will only be required by the async transport. If more async transports are expected,
another shared superclass can be created.

GH-4568

Add necessary type annotations to the core HttpTransport to accomodate for async transport.

GH-4568

Add an abstract bass class for implementation of the background worker. This was done to provide a shared interface for the current
implementation of a threaded worker in the sync context as well as the upcoming async task-based worker implementation.

GH-4578

Add a new factory method instead of direct instatiation of the threaded background worker.
This allows for easy extension to other types of workers, such as the upcoming task-based async worker.

GH-4578

Add a new flush_async method to worker ABC. This is necessary because the async transport cannot use a
synchronous blocking flush.

GH-4578

Move the flush_async down to the concrete subclass to not break existing testing. This makes sense,
as this will only really be needed by the async worker anyway and therefore is not shared logic.

GH-4578

Coroutines have a return value, however the current function signature for the worker methods does not
accomodate for this. Therefore, this signature was changed.

GH-4578

Add a new implementation of the worker interface, implementing the worker as an async task. This is
to be used by the upcoming async transport.

GH-4581

Refactor the flush method in the async worker to use the async_flush coroutine.

GH-4581

…unctions

Add a check to see wheter callbacks are awaitable coroutines or functions, as coroutines need to be awaited.

GH-4581

…coroutines

Coroutines do not return None, therefore it is necessary to consider this in the callback parameter of the worker. Previously,
only callbacks with return Type None were accepted.

GH-4581

GH-4581

GH-4581

Enable concurrent callbacks on async task worker by firing them as a task rather than awaiting them. A done callback handles the necessary queue and exception logic.

GH-4581

Changed kill to also use the _TERMINATOR sentinel, so the queue is still drained to this point on kill instead of cancelled immediately. This should also fix potential race conditions with flush_async.

GH-4581

Add proper type annotation to worker task list to fix linting problems

GH-4581

Add an implementation of Transport to work with the async background worker and HTTPCore async.

GH-4582

Async Transport now properly checks for the presence of the event loop in capture_envelop, and drops items
in case the event loop is no longer running for some reason.

GH-4582

Implement a kill method that properly shuts down the async transport. The httpcore async connection pool needs
to be explicitly shutdown at the end of its usage.

GH-4582

Fix type errors resulting from async override and missing type definition in the async transport.

GH-4582

GH-4582

GH-4582

Refactor transport code based on PR suggestions. Furthermore, add a requirement for the async extra in setup.py

GH-4582

…egration

GH-4601

GH-4601

GH-4601