Move TraceContext utilities to an SPI/common tracing API

StarTree Pinot needs to instrument plugin code that runs in the Pinot server query path using TraceContext and TraceCallable. Today both classes live under org.apache.pinot.core.util.trace in pinot-core, so plugins that want to emit query trace entries must depend on pinot-core with provided scope even though the abstraction is cross-cutting instrumentation rather than core server implementation.

Request:
- Move or expose TraceContext and TraceCallable through a stable tracing API in pinot-spi or pinot-common.
- Keep source/binary compatibility shims from the current pinot-core package if needed.
- Allow Pinot plugins to depend on the narrower API module instead of pinot-core for query trace instrumentation.

This would reduce plugin dependency surface and make trace instrumentation usable from modules that should not compile against the full pinot-core implementation jar.

Start by locating TraceContext and TraceCallable under org.apache.pinot.core.util.trace and inspecting their uses in Pinot plugins and query-path code. Review the pinot-spi and pinot-common module boundaries and compatibility needs; done means plugins can use query trace instrumentation through the narrower API without depending on pinot-core, while existing package users remain compatible if required.

Written by the indexing model from the issue text.