Add DirCon loopback integration test and CI workflow

[cagnulein]

Motivation

• Add an integration test to validate DirCon server/client loopback behavior and telemetry delivery to prevent regressions in DirCon connectivity.

Description

• Add tst/Devices/dirconloopbacktestsuite.cpp and tst/Devices/dirconloopbacktestsuite.h which start a local fakebike DirCon server and a wahoodirconbike client, then assert successful handshake and non-zero telemetry (watts/cadence/speed).
• Update tst/qdomyos-zwift-tests.pro to include the new test source and header in the test target.
• Add a GitHub Actions workflow .github/workflows/dircon-loopback.yml that installs Qt dependencies, builds the static library and test binary, and runs the DirCon loopback test on ubuntu-24.04.

Testing

• CI job DirCon loopback integration test is configured to run ./qdomyos-zwift-tests --gtest_filter=DirconLoopbackTestSuite.* after building the code and dependencies.
• No automated test run results are included in this change; the workflow is added and ready to execute in CI.

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Codex Task