fix(DataStore): serialize IncomingAsyncSubscriptionEventPublisher events

[lawmicha]

Issue #

#2982 (comment)

Description

Before the PR changes, the publisher would emit events concurrently which caused some of them to be missed by the subscriber even though the subscriber applied back pressure to process one event at a time (demand of max(1)). For more details regarding back-pressure, see https://developer.apple.com/documentation/combine/processing-published-elements-with-subscribers

The change, to publish the events though the same TaskQueue ensures that the events are properly buffered and sent only when the subscriber demands for it.

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

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

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (f64c471) 67.90% compared to head (1f194d2) 67.98%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
...Sync/IncomingAsyncSubscriptionEventPublisher.swift	76.92%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3489      +/-   ##
==========================================
+ Coverage   67.90%   67.98%   +0.07%     
==========================================
  Files        1080     1080              
  Lines       36406    36415       +9     
==========================================
+ Hits        24723    24755      +32     
+ Misses      11683    11660      -23     

Flag	Coverage Δ
API_plugin_unit_test	67.23% <ø> (ø)
AWSPluginsCore	64.18% <ø> (ø)
Amplify	48.12% <ø> (+0.01%)	⬆️
Analytics_plugin_unit_test	81.16% <ø> (ø)
Auth_plugin_unit_test	78.98% <ø> (+0.02%)	⬆️
CoreMLPredictions_plugin_unit_test	59.44% <ø> (ø)
DataStore_plugin_unit_test	80.72% <76.92%> (+0.30%)	⬆️
Geo_plugin_unit_test	70.75% <ø> (ø)
Logging_plugin_unit_test	63.34% <ø> (ø)
Predictions_plugin_unit_test	37.16% <ø> (ø)
PushNotifications_plugin_unit_test	87.13% <ø> (ø)
Storage_plugin_unit_test	77.51% <ø> (ø)
unit_tests	67.98% <76.92%> (+0.07%)	⬆️

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