fix(translate): accept structured custom tool outputs

[M1k0t0]

Summary

Responses custom tool results were rejected whenever output was an array, even when it contained only text. This could interrupt Codex after a successful tool call with Cannot translate multimodal custom_tool_call_output.

Handle custom_tool_call_output through the same output conversion as function_call_output in both the Chat Completions and Anthropic Messages translators. This supports text arrays, empty results, and images while preserving tool-call IDs and result ordering. Chat Completions places images after the complete tool-result group; Anthropic Messages keeps them inside tool_result and preserves incomplete status.

Regression coverage includes structured output conversion, image handling, unsupported file outputs, and two-turn HTTP continuations using previous_response_id through both target protocols.

Validation

All 125 tests across the two request translator suites and the Responses HTTP suite passed.