[shortfin llm] Add base classes for tracing

[renxida]

This PR adds some framework-ey classes for tracing.

Coming next:

• A small PR that adds some tracing for cache alloc - dealloc, just to get some minimal-useful-tracing going.
• [shortfin llm] Add trace_fn decorator for tracing the execution of a function #1073: syntax sugar @tracy_fn(function_name, frame_args) for tracing functions.
• [shortfin llm] Add tracing with tracy #1074: tracy tracing backend