refactor(ai): improve select retry ctx logic

[rickstaa]

What does this pull request do? Explain your changes. (required)

This commit refines context handling in the orchestrator selection loop for idiomatic Go and enhanced propagation of parent cancellations.

Specific updates (required)

• Improves contex handeling logicai_process.go.

How did you test each of these updates (required)

I ran the O onchain and verified the timeout still successfully triggered a ctx cancel and returned out of the loop.

Does this pull request close any open issues?

Fixes usefull improvements remakrs made by @yondonfu in https://github.com/livepeer/go-livepeer/pull/3030#discussion_r1588499005.

Checklist:

• [x] Read the contribution guide
• [x] make runs successfully
• [ ] All tests in ./test.sh pass
• [x] README and other documentation updated
• [ ] Pending changelog updated