[v6.0] fix(ai): enforce timeout.stepMs for the whole step in streamText

[gr2m]

Manual backport of #15840 to release-v6.0. The stream-text.ts internals diverged between v6 and main, so the fix was ported by hand: keep the step/chunk timers armed after step setup returns (they were disarmed in a finally immediately), clear them via the merged abort signal, and clear eagerly only when setup throws. Tests adapted to v6 idioms (MockLanguageModelV3, stepCountIs, no TimeoutError abort reason since #14943 is not on v6 yet). Full stream-text suite passes locally (349/349).

Part of the v6.0 backport tracking issue #16767.

[github-actions]

⚠️ Backport to release-v5.0 created but has conflicts: #16828

[github-actions]

🚀 Published in:

Package	Version
ai	6.0.221 github npm
@ai-sdk/alibaba	1.0.36 github npm
@ai-sdk/amazon-bedrock	4.0.131 github npm
@ai-sdk/angular	2.0.222 github npm
@ai-sdk/anthropic	3.0.95 github npm
@ai-sdk/anthropic-aws	1.0.17 github npm
@ai-sdk/assemblyai	2.0.44 github npm
@ai-sdk/azure	3.0.86 github npm
@ai-sdk/baseten	1.0.61 github npm
@ai-sdk/black-forest-labs	1.0.45 github npm
@ai-sdk/bytedance	1.0.25 github npm
@ai-sdk/cerebras	2.0.64 github npm
@ai-sdk/cohere	3.0.46 github npm
@ai-sdk/deepgram	2.0.43 github npm
@ai-sdk/deepinfra	2.0.62 github npm
@ai-sdk/deepseek	2.0.46 github npm
@ai-sdk/elevenlabs	2.0.43 github npm
@ai-sdk/fal	2.0.44 github npm
@ai-sdk/fireworks	2.0.66 github npm
@ai-sdk/gateway	3.0.145 github npm
@ai-sdk/gladia	2.0.43 github npm
@ai-sdk/google	3.0.90 github npm
@ai-sdk/google-vertex	4.0.158 github npm
@ai-sdk/groq	3.0.49 github npm
@ai-sdk/huggingface	1.0.60 github npm
@ai-sdk/hume	2.0.43 github npm
@ai-sdk/klingai	3.0.28 github npm
@ai-sdk/langchain	2.0.229 github npm
@ai-sdk/llamaindex	2.0.221 github npm
@ai-sdk/lmnt	2.0.43 github npm
@ai-sdk/luma	2.0.43 github npm
@ai-sdk/mcp	1.0.60 github npm
@ai-sdk/mistral	3.0.47 github npm
@ai-sdk/moonshotai	2.0.34 github npm
@ai-sdk/open-responses	1.0.26 github npm
@ai-sdk/openai	3.0.82 github npm
@ai-sdk/openai-compatible	2.0.58 github npm
@ai-sdk/perplexity	3.0.44 github npm
@ai-sdk/prodia	1.0.42 github npm
@ai-sdk/provider-utils	4.0.37 github npm
@ai-sdk/quiverai	1.0.10 github npm
@ai-sdk/react	3.0.223 github npm
@ai-sdk/replicate	2.0.43 github npm
@ai-sdk/revai	2.0.43 github npm
@ai-sdk/rsc	2.0.221 github npm
@ai-sdk/svelte	4.0.221 github npm
@ai-sdk/togetherai	2.0.63 github npm
@ai-sdk/valibot	2.0.38 github npm
@ai-sdk/vercel	2.0.60 github npm
@ai-sdk/voyage	1.0.14 github npm
@ai-sdk/vue	3.0.221 github npm
@ai-sdk/xai	3.0.104 github npm