fix(openai): filter function_call blocks in token counting

[sujalmh]

The Responses API returns messages with function_call content blocks which cause get_num_tokens_from_messages to raise a ValueError: Unrecognized content block type. This occurs because the token counter internally uses the chat/completions format logic, which does not recognize these blocks.

This PR updates _format_message_content to filter out function_call blocks when formatting messages for the chat/completions API (which includes the token counter). These blocks are redundant for token counting as the actual tool calls are already handled via the separate tool_calls field, ensuring accurate counts without errors.

Fixes #34378

Breaking Changes: None.

[codspeed-hq]

CodSpeed Performance Report

Merging #34396 will not alter performance

_{Comparing sujalmh:fix/token-counter-function-call (c21a249) with master (71778cb)}

Summary

✅ 6 untouched
⏩ 28 skipped¹

Footnotes

1. 28 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩