re_test_mocks

In-process server doubles (MockOtlpCollector, MockPostHog) used by tests that need to capture outbound OTel/PostHog traffic.

Both mocks are full implementations of the wire protocols they stand in for — a tonic gRPC TraceService for OTLP and an axum HTTP handler for PostHog's /batch endpoint. They run on ephemeral ports in the test process, capture every request, and expose notification-driven wait_for(…) and received() accessors so tests don't have to poll. The assert_sink_empty! macro is the companion no-traffic assertion.

The crate root re-exports nothing; consumers reach into the submodules directly via re_test_mocks::otlp::MockOtlpCollector and re_test_mocks::posthog::MockPostHog.