[doc] feat: Document adapter merge verification in stream_adapter_weights example

[yaoyu-33]

Description

Adds documentation to the stream_adapter_weights.py example script explaining the verification feature.

Changes

• Added a "Verification" section to the module docstring that explains:
  • The verification is enabled by default (disable with --no-verify)
  • What the verification does: checks that manually merging adapter weights (lora_A, lora_B) onto base weights using the LoRA formula produces the same result as exporting with merge_adapter_weights=True
  • This ensures the adapter streaming and merge-back paths are mathematically consistent

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