Add support for strict=1 parameter in import API for enhanced validation

[Copilot]

This PR implements support for the strict=1 parameter in Mixpanel's import API to enable enhanced validation as recommended in the official documentation.

Features Added

Global Strict Configuration

Enable strict validation for all import requests:

// During initialization
const mixpanel = Mixpanel.init('token', { secret: 'secret', strict: true });

// Or after initialization
mixpanel.set_config({ strict: true });

Method-Level Strict Options

Enable strict validation for individual requests:

// For single event import
mixpanel.import('event_name', new Date(), { distinct_id: 'user123' }, { strict: true });

// For batch import
mixpanel.import_batch(events, { strict: true }, callback);

Benefits

When strict=1 is enabled, the import API will:

• Validate all supplied events before processing
• Return detailed error information (400 status) if validation fails
• Still ingest events that pass validation when others fail
• Provide $insert_ids of invalid events for debugging

This is especially valuable in production environments for identifying and debugging event formatting issues.

Implementation Details

• Added strict option to DEFAULT_CONFIG with default value false
• Modified send_request to append strict=1 query parameter for import endpoints
• Updated import() and import_batch() methods to accept strict options
• Enhanced TypeScript definitions with new ImportOptions interface
• Maintained full backward compatibility with existing API signatures

Testing

• All existing tests continue to pass (178 total)
• Added comprehensive test coverage for new functionality
• Verified backward compatibility with all existing usage patterns
• Tested both global and method-level strict configurations

Fixes #233.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.mixpanel.com
  • Triggering command: node (vitest) (dns block)
  • Triggering command: node /tmp/test_strict_functionality.js (dns block)
  • Triggering command: node /tmp/test_backward_compatibility.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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[austinpray-mixpanel]

@tdumitrescu not bad at first glance