[AMSDK-11543] Fix data race in Extension container

[praveek]

Fix a data race in Extension container where lastProcessedEvent is accessed from different threads.

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #684 (0a67679) into dev-v3.2.4 (69b84a3) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           dev-v3.2.4     #684      +/-   ##
==============================================
+ Coverage       85.31%   85.34%   +0.03%     
==============================================
  Files             105      105              
  Lines            4644     4652       +8     
==============================================
+ Hits             3962     3970       +8     
  Misses            682      682              

[sbenedicadb]

looks good.