Update secure session SendMessage() unit test harness to do asynchronous send an...

[todo]

connectedhomeip/src/protocols/secure_channel/CASESession.cpp

Lines 396 to 406 in 7544281

	// TODO: Update secure session SendMessage() unit test harness to do asynchronous send and receives.
	mState = kSentSigma1;
	// Call delegate to send the msg to peer
	ReturnErrorOnFailure(mExchangeCtxt->SendMessage(Protocols::SecureChannel::MsgType::CASE_Sigma1, std::move(msg_R1),
	SendFlags(SendMessageFlags::kExpectResponse)));
	ChipLogDetail(SecureChannel, "Sent Sigma1 msg");
	return CHIP_NO_ERROR;
	}

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This issue was generated by todo based on a TODO comment in 7544281 when #9904 was merged. cc @pan-apple.