feat: add SSH key rotation functionality

[arb8020]

Summary

• Add comprehensive SSH key management to bring TypeScript SDK to parity with Python SDK
• Implement sshKey() and sshKeyRotate() methods on Instance class with proper TypeScript interfaces
• Include comprehensive integration and unit tests mirroring Python SDK test suite

Key Changes

• InstanceSshKey interface: Proper typing for SSH key objects with object, private_key, public_key, and password fields
• Instance.sshKey(): Retrieve current SSH key details for instance
• Instance.sshKeyRotate(): Generate new SSH key, invalidating the old one
• Comprehensive tests: Both integration tests (mirroring Python SDK) and unit tests for type verification
• Jest configuration: Proper test setup for TypeScript with 5-minute timeout for integration tests

Implementation Details

Based on Python SDK commit 58d2b66 "rotation for ssh keys", this implementation:

• Follows established SDK patterns for async methods and error handling
• Uses proper TypeScript interfaces for type safety
• Includes comprehensive JSDoc documentation
• Maintains compatibility with existing SSH connection methods

Test Coverage

• Unit tests verify method existence, API calls, and TypeScript interfaces
• Integration tests cover real-world scenarios including SSH connection validation
• Tests for uniqueness across multiple rotations and raw HTTP API endpoint access

Test plan

• Unit tests pass (npm test test/unit/sshkey.test.ts)
• Build succeeds (npm run build)
• Integration tests written (requires MORPH_API_KEY environment variable to run)
• Code follows existing patterns and conventions
• TypeScript types export correctly

Note: Integration tests require MORPH_API_KEY environment variable but are comprehensive and mirror the Python SDK test suite exactly.

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