fix: preserve LLM delta ordering metadata

[dannote]

Summary

• add optional ordering/correlation fields to ai.llm.delta
• propagate runtime seq, run_id, request_id, and iteration from ReAct deltas
• propagate available worker metadata from ChainOfThought deltas
• document that consumers should order deltas by seq within a call_id when exact transcript reconstruction matters

Why

Runtime-backed strategies already have ordered runtime events, but derived ai.llm.delta signals dropped that metadata. Consumers receiving deltas out of delivery order could not reconstruct the intended stream.

Tests

• mix test test/jido_ai/signal_test.exs test/jido_ai/strategy/react_test.exs test/jido_ai/strategy/chain_of_thought_test.exs
• mix test.fast
• mix compile --warnings-as-errors