[fix][client-cpp] Fix TypedMessageTest to use receiveAsync<T> template overload with decoder

[geniusjoe]

Fixes #466

Master Issue: #149

Motivation

The TypedMessageTest.testReceive test was using receiveAsync incorrectly. It called the untyped receiveAsync(const ReceiveCallback&) overload (where ReceiveCallback is std::function<void(Result, const Message&)>), but the lambda's parameter was declared as const TypedMessage<int>& — a derived class reference. Since the actual argument passed at runtime is const Message&, this relies on an implicit downcast from base to derived, which is not guaranteed to work across compilers.

GCC 11+ happens to be permissive about this implicit conversion when constructing std::function from a lambda (it does not strictly enforce contravariance on parameter types during type erasure), so the code compiled successfully. However, GCC 8.x does not accept this conversion, causing a compilation failure (see #466).

The fix is to use the proper typed template overload consumer.receiveAsync<int>(callback, intDecoder), which internally constructs TypedMessage<int>{msg, decoder} and passes it to the callback. This is both the intended API usage and portable across all GCC versions.

Modifications

• Changed consumer.receiveAsync(...) to consumer.receiveAsync<int>(..., intDecoder) to use the correct typed template overload.
• Simplified the callback by directly assigning msg = receivedMsg instead of manually constructing TypedMessage<int>{receivedMsg, intDecoder}, since the decoder is now passed to receiveAsync<T> and applied internally.

Verifying this change

This change is already covered by existing tests, such as TypedMessageTest.testReceive which validates the typed message receive flow including receiveAsync<int>.

Documentation

• doc-not-needed
  (This is a test fix only, no public API changes.)

[Copilot]

Pull request overview

Fixes TypedMessageTest.testReceive to use the correct typed Consumer::receiveAsync<T>(callback, decoder) overload so the callback receives a TypedMessage<T> without relying on non-portable implicit downcasting behavior (fixes build issues on GCC 8.x as described in #466).

Changes:

• Update TypedMessageTest.testReceive to call consumer.receiveAsync<int>(..., intDecoder) instead of the untyped overload.
• Simplify the async receive callback to assign the already-decoded TypedMessage<int> directly.

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