Fix lint and format on langchain samples

[Radhika Gupta (rads-1996)]

No description provided.

[Copilot]

Pull request overview

This PR updates the LangChain sample scripts to better conform to repo linting/formatting rules and improve readability/consistency in the sample configuration sections.

Changes:

• Reformats samples and replaces lowercase config variables with module-level constants (e.g., ENDPOINT, API_KEY, MODEL_NAME).
• Cleans up sample setup blocks (e.g., configure_azure_monitor(...) formatting; removes unused imports).
• Adjusts comments/documentation blocks in samples to reflect current intended distro direction.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
samples/langchain/sample_opentelemetry.py	Reformats header comments and replaces config vars with constants; updates setup comments and instrumentation teardown formatting.
samples/langchain/sample_langchain_azure.py	Removes unused imports; reformats config/setup and some nested structures for readability; uses constants for endpoint/key/model.
samples/langchain/sample_arise_langchain.py	Reformats Azure Monitor configuration and replaces config vars with constants; improves readability of the multimodal message structure.

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