feat: add batch delete documents support to API, SDK, CLI, and tests

[mdehsan873]

• Added /documents/batch_delete API endpoint for deleting multiple documents at once
• Implemented service method to handle deletion and error resilience
• Updated SDK (sync + async) to expose batch_delete_documents()
• Added CLI command: morphik batch-delete <doc_ids...>
• Added test cases in both async and sync SDKs to verify batch deletion
• Closes Add batch delete documents endpoint #78

[jazzberry-ai]

Bug Report

Name	Severity	Example test case	Description
Missing CLI command	Low	Attempt to use the morphik batch-delete command.	The patch description mentions a CLI command for batch deletion, but there's no code related to the CLI in the provided diff.
No limit on batch size	Medium	Submit a request to delete a very large number of documents.	There's no limit on the number of documents that can be deleted in a single batch. A malicious user could submit a request to delete a very large number of documents, potentially causing performance problems or even a denial-of-service.
Incorrect telemetry metadata	High	Use the batch_delete_documents API endpoint.	The document_delete_metadata function in core/services/telemetry.py is not designed to handle batch deletion. It will likely raise a KeyError or only capture the first document ID in the list, resulting in inaccurate telemetry data.
Generic error message in API	Low	Call batch delete API with a bad document id	The API endpoint returns a generic "Batch deletion failed" error message. It would be more helpful to provide more specific information about the error.

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[CLAassistant]

All committers have signed the CLA.

[jazzberry-ai]

Bug Report

Name	Severity	Example test case	Description
Incomplete Error Reporting in Batch Document Deletion	Medium	Create two documents, attempt to batch delete one that will fail.	The batch document deletion function does not explicitly inform the user about documents that failed to delete.

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[mdehsan873]

@ArnavAgrawal03 or @Adityav369 Can you please review this PR?