Allow for Enabling/Disabling KVP using Config

[peytonr18]

This PR introduces the ability to enable or disable KVP logging through the telemetry.kvp_diagnostics field in the configuration.

Changes

• The setup_layers function now checks config.telemetry.kvp_diagnostics before initializing emit_kvp_layer.
• If kvp_diagnostics = false, emit_kvp_layer is set to None, ensuring no logs are written to the EmitKVPStruct.
• If config is None, the default behavior (true) is maintained.
• Added a unit test in kvp.rs to validate that no data is written when KVP is disabled.

Key Point: Config Tracing & KVP Behavior

• Before the config is loaded, setup_layers is called once with None, meaning the config values will still be written to KVP. If kvp_diagnostics = false, KVP logging will stop after the second call to setup_layers, since the new subscriber overrides the previous one.

Dependency on probertson-cache-vm-id-logging-new

This PR is based on probertson-cache-vm-id-logging-new, as that branch introduces passing Config into setup_layers, which is required for this logic.

Next Steps

• Merge probertson-cache-vm-id-logging-new first.
• Then merge this PR to introduce configurable KVP diagnostics.

Resolves #152.