[codex] Add invalid tool call recovery hook

[gold-silver-copper]

Summary

• Add InvalidToolCallHookAction and PromptHook::on_invalid_tool_call for model-emitted unknown or disallowed tool calls.
• Preserve the default fail-fast behavior by returning PromptError::UnknownToolCall unless the hook opts into recovery.
• Allow hooks to return retry feedback as a synthetic tool result, continuing the prompt loop without executing invalid tool calls or peer tool calls from the invalid assistant turn.
• Wire the hook into non-streaming prompts, completed streaming tool calls, and streaming tool-name deltas while keeping invalid calls away from normal on_tool_call and tool execution.
• Add regression coverage for non-streaming retry, streaming completed-call retry, and streaming name-delta retry.

Notes

This builds on the tool-call validation added in #31 / upstream 0xPlaygrounds#1823. The default remains strict fail-fast; recovery is opt-in through the new hook action.

Validation

• cargo fmt
• cargo test -p rig-core agent::prompt_request:: -- --nocapture
• cargo check -p rig-core
• git diff --check