feat: Implement transaction context

[askpt]

Transaction Context

This pull request introduces transaction context propagation to the OpenFeature library. The changes include adding a new interface for transaction context propagation, implementing a no-op and an AsyncLocal-based propagator, and updating the API to support these propagators.

Related Issues

Fixes #243

Notes

Transaction Context Propagation:

• src/OpenFeature/Api.cs: Added a private field _transactionContextPropagator and a lock for thread safety. Introduced methods to get and set the transaction context propagator, and to manage the transaction context using the propagator. [1] [2]
• src/OpenFeature/AsyncLocalTransactionContextPropagator.cs: Implemented the AsyncLocalTransactionContextPropagator class that uses AsyncLocal<T> to store the transaction context.
• src/OpenFeature/NoOpTransactionContextPropagator.cs: Implemented a no-op version of the ITransactionContextPropagator interface.
• src/OpenFeature/Model/ITransactionContextPropagator.cs: Defined the ITransactionContextPropagator interface responsible for persisting transaction contexts.

API Enhancements:

• src/OpenFeature/Api.cs: Updated the ShutdownAsync method to reset the transaction context propagator.
• src/OpenFeature/OpenFeatureClient.cs: Modified the EvaluateFlagAsync method to merge the transaction context with the evaluation context.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.67%. Comparing base (e14ab39) to head (64f5c68).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #312      +/-   ##
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+ Coverage   85.30%   85.67%   +0.36%     
==========================================
  Files          36       38       +2     
  Lines        1477     1515      +38     
  Branches      150      153       +3     
==========================================
+ Hits         1260     1298      +38     
  Misses        187      187              
  Partials       30       30              

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[lukas-reining]

Nice start! Left some thoughts and references to how we are doing it in the other languages.

[askpt]

Nice start! Left some thoughts and references to how we are doing it in the other languages.

Thanks for the review @lukas-reining. I based the implementation on the JS client. I'll look into more detail on the Java version instead.