Job_chat: remove redundant job code edits

[hanna-paasivirta]

Short Description

Removes unnecessary second apply_code_edits in job_chat.

Implementation Details

The streaming path applies edits mid-stream to emit suggested_code in the changes event, but the post-stream path was then calling parse_and_apply_edits in all scenarios and redoing the same edits. Now we cache the streaming-resolved result on self and skip the post-stream apply when it's already been run. The non-streaming path still falls through to parse_and_apply_edits as before.

AI Usage

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• Code generation (copilot but not intellisense)
• Learning or fact checking
• Strategy / design
• Optimisation / refactoring
• Translation / spellchecking / doc gen
• Other
• I have not used AI

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