Acquire/Release Event Loop

[xiazhvera]

Issue #, if available:

Description of changes:

• What does this PR do
  This PR introduces APIs to acquire and release event loops, by acquiring and releasing the event loop group (ELG) that the event loop belongs to. If the event loop does not belong to any group, the acquire operation will fail. However, this case should never occur in practice, as users are expected to interact with the event loop group API directly.

• Why do we need this
  Event loops are not ref-counted. For asynchronous APIs like the Dispatch Queue, it is necessary to retain a reference to the ELG ensures the event loop isn’t destroyed while async work is still pending. Besides, In cases where we need to process tasks on an event loop outside the context of a channel (e.g., request response client), we must ensure the event loop remains alive independently of the channel or channel bootstrap.
  These new APIs help to keep the event loop alive as needed.

Also merged with a previous similar PR: #536

Ideally socket should also get updated to acquire event loop (

aws-c-io/include/aws/io/socket.h

Line 159 in 7e75f17

struct aws_event_loop *event_loop;

), however, we frequently set/unset event loop in posix socket make things complicated (https://github.com/awslabs/aws-c-io/blob/get_eventloop_group/source/posix/socket.c#L449). I will leave the socket as it is for now.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.74%. Comparing base (7c00720) to head (b59954d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #725      +/-   ##
==========================================
+ Coverage   78.60%   78.74%   +0.14%     
==========================================
  Files          30       30              
  Lines        6380     6385       +5     
==========================================
+ Hits         5015     5028      +13     
+ Misses       1365     1357       -8     

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[sbSteveK]

Optional name change for clarity. Otherwise looks solid.

[bretambrose]

Let's talk about this

[waahm7]

Similar PR: #536. I don't know why that was not merged.

There was concern about the original API was misleading—it suggested that it was acquiring an event loop directly, which is not accurate. In reality, the operation acquires the event loop group associated with the event loop, not the event loop itself. To avoid confusion and better reflect the actual behavior, we have updated the API name to clearly indicate that it acquires the event loop group through the event loop.