Complete the issue #38 CMake gating so protobuf can be excluded #108

Parent

Part of #102

What to build

A firmware build in which protobuf and Abseil can actually be excluded once nothing needs them. Completing the CMake gating tracked by issue #38: the exporter Kconfig symbols already landed, leaving the conditionals that stop the OTLP HTTP exporter and the protobuf setup from being pulled in unconditionally.

Target: this repository, on its own branch. Independent of all JsonWriter work and can start immediately.

This is a prerequisite for the protobuf-free switchover: without it, nothing is excluded from the build regardless of what the exporters require.

Acceptance criteria

• The OTLP HTTP exporter and the protobuf setup are included only when the corresponding Kconfig symbols select them
• A build with the OTLP exporters deselected compiles and links
• The existing traces example still builds and runs unchanged in the default configuration
• Binary inspection confirms protobuf is not compiled when deselected

Blocked by

• None (can start immediately)