Transparent Virtual Echelon bridge: disable QZ session injection and add proxy logging

[cagnulein]

Motivation

• Allow an external Echelon client to own the full proprietary session while QZ remains a transparent bridge for notifications and metrics.
• Prevent QZ from injecting polls, ERG/resistance changes, or start/stop commands when operating in transparent virtual Echelon mode.
• Improve debugging visibility for virtual Echelon traffic between client, QZ, and the physical bike.

Description

• Added transparentVirtualEchelonBridgeEnabled() and its declaration in echelonconnectsport.h to centralize the transparent-bridge enablement check.
• Skip btinit() during initialization when transparent virtual Echelon bridge mode is active by checking transparentVirtualEchelonBridgeEnabled() in update().
• Prevent QZ from sending polls, changing resistance, or issuing start/stop commands when transparent mode is enabled by early-returning from update() after metrics are consumed.
• Added debug logging for Echelon traffic: TX logging in proxyVirtualBikeCommand() and RX/TX logging in characteristicChanged() and virtualbike::relayEchelonPacket() to surface client↔bike packets.

Testing

• Project build completed successfully with the changes using the normal build pipeline (cmake/build system).
• Automated unit tests were executed via the project test runner (ctest) and passed.
• Automated integration tests exercising virtual-device Echelon proxy behavior were run and passed, verifying that QZ does not inject commands while transparent mode is enabled.

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Codex Task

[cagnulein]

#4938