Add configurable escalation for repeated tool-call loops

[andrew-ellis-engineering]

Closes #3700

Adds configurable turn-level escalation for repeated identical tool-call patterns, with deterministic interrupt behavior, logging, and tests.

[chengyongru]

Thanks for the PR. Closing this for similar reasons as #3701:

1. Already covered — max_iterations caps loop length; repeated_external_lookup_error handles external lookups. Turn-level escalation for identical calls is solving a problem that hasn't been reported by users.

2. ToolLoopEscalationInterrupt unconditionally raises RuntimeError, ignoring the fail_on_tool_error flag — once a threshold is hit, the entire run is killed with no graceful fallback.

3. Duplicates Guard repeated identical local tool calls in a single turn #3701 — both PRs add near-identical signature/count logic and thread the same parameter dicts through _run_tool/_execute_tools.

4. The repeated_tool_call_escalation_threshold field is added to AgentRunSpec but has no config-layer exposure, so it's unreachable for actual users.

Appreciate the effort though!