bug: mixed function-call model turns are not recognized as tool turns

### What happened?

`isFunctionCall()` in `packages/core/src/utils/messageInspectors.ts` currently requires every part in a model turn to contain `functionCall`.

That misses valid mixed model turns containing a function call alongside another part, for example a thought plus a tool call.

This matters in `ClassifierStrategy`, which removes tool-related turns from routing history using `isFunctionCall()` and `isFunctionResponse()`.

`isFunctionResponse()` already detects a function response among sibling parts, so the subsequent function-response turn is removed while the mixed model function-call turn is retained. The classifier can therefore receive an unmatched function-call turn.

### Expected behavior

A model turn containing at least one `functionCall` should be recognized as a function-call turn even when sibling thought/text parts are present.

### Suggested fix

Use `content.parts.some((part) => !!part.functionCall)` and add regression coverage for a mixed thought + function-call turn.

Found by source audit on current main.

Start in packages/core/src/utils/messageInspectors.ts and compare isFunctionCall() with isFunctionResponse(). Trace how ClassifierStrategy uses these inspectors, then add regression coverage for a mixed thought and function-call turn. Done means any model turn containing at least one functionCall is recognized and the regression coverage passes.

Written by the indexing model from the issue text.