fix: move routed experts helpers to response utils

[S1ro1]

Summary

• move routed expert parsing/truncation helpers out of verifiers.clients and into existing response utilities
• update OpenAI clients to import routed expert parsing from verifiers.utils.response_utils

Verification

• uv run ruff check verifiers/clients/openai_chat_completions_client.py verifiers/clients/openai_completions_client.py verifiers/utils/response_utils.py

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Note

Low Risk
Primarily a namespace refactor moving parse_routed_experts/truncate_routed_experts without behavioral changes; risk is limited to potential import/path issues affecting token parsing/truncation.

Overview
Refactors routed-experts handling by moving parse_routed_experts and truncate_routed_experts out of verifiers.clients.routed_experts (module removed) into verifiers.utils.response_utils.

Updates OpenAI chat/completions clients and response token parsing to import parse_routed_experts from the utils module, consolidating routed-experts parsing/truncation alongside other response utilities.

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