Migrate Azure Batch provider to azure-batch 15.x (track 2 SDK)

[wjddn279]

Closes: #66466

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)
  claude code (4.7 Opus)

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[potiuk]

@wjddn279 This draft PR has had no activity for 2 weeks. Closing to keep the queue clean.

You are welcome to reopen and continue when you're ready. If you'd like to pick it back up, please rebase onto the current main branch first.

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Drafted-by: Claude Code (Opus 4.7); reviewed by @potiuk before posting