feat: add cursor.count() deprecation error

[h3n4l]

Summary

• Return a helpful error message when cursor.count() is used
• Direct users to use countDocuments() or estimatedDocumentCount() instead

Error Message

unsupported operation "count()": MongoDB drivers deprecate their respective cursor and collection count() APIs in favor of countDocuments() and estimatedDocumentCount()

Rationale

MongoDB drivers deprecate their respective cursor and collection count() APIs in favor of new APIs that correspond to countDocuments() and estimatedDocumentCount(). Rather than supporting a deprecated method, we return a clear error message guiding users to the recommended alternatives.

Test plan

• Integration test verifies deprecation error is returned
• Error message contains count(), countDocuments(), and estimatedDocumentCount()
• All existing tests pass
• Linting clean

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds support for the deprecated MongoDB cursor.count() operation to enable backward compatibility with existing MongoDB shell scripts. The implementation allows counting documents matching a find() query while respecting skip() and limit() cursor modifiers.

Changes:

• Added opCount operation type for cursor count operations
• Implemented executeCount() function that uses CountDocuments() with skip/limit options
• Added comprehensive test coverage for various count scenarios including filters, skip/limit modifiers, empty collections, and bracket notation

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
translator.go	Added opCount constant and translator logic to detect count() method calls on cursors
executor.go	Implemented executeCount() function that executes count operations with filter, skip, and limit support
executor_test.go	Added 5 comprehensive test functions covering basic count, filters, skip/limit, empty collections, and bracket notation

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