Remove deprecated methods in gen-ai utils

[lmolkova]

we should at some point remove all the deprecated methods from util-genai

[bhumikadangayach]

I'd like to take this on. Checked usage across the repo — none of the instrumentation packages or the shared test-util package actually call the deprecated methods (start_llm, stop_llm, fail_llm, start_embedding, start_tool, start_workflow, start_agent, start_remote_agent) anymore; the only remaining references are in docstrings/comments. So this should be a clean removal with no cross-package migration needed. I'll remove the 8 deprecated methods and their docstrings from handler.py, plus the deprecated note in _inference_invocation.py, and update any docstring cross-references. Let me know if there's a deprecation-window policy I should respect (e.g. wait for a release cycle) before I open a PR.

[bhumikadangayach]

Following up on this — I've gone ahead and done the removal locally (all 9 deprecated methods: start_inference, start_llm, start_embedding, start_tool, start_workflow, stop_llm, fail_llm, start_invoke_local_agent, start_invoke_remote_agent — turns out there were 9, not 8, start_inference was one I'd initially missed). All green locally (234 tests passing, typecheck/precommit clean). Happy to open the PR whenever's appropriate — just didn't want to do so without knowing if there's a deprecation window you'd want respected first (e.g. wait a release cycle before removing).

[bhumikadangayach]

Since I hadn't heard back on the deprecation-window question, I went ahead and opened this as a draft PR (#300) so the completed work is available whenever you have a chance to look at it. I'm not looking for a review yet—I just wanted to get it off my local branch and make it easier to find. If you'd prefer a different approach or to wait for the next release cycle, I'm happy to make those changes. Just let me know what you think when you have a moment.