feat: add graceful fallback for isows dependency

[mandarini]

What kind of change does this PR introduce?

Bug fix - adds compatibility for server environments where isows is not available.

What is the current behavior?

RealtimeClient fails when isows is not available in server environments, causing Cannot find module 'isows' errors and preventing the client from being instantiated.

What is the new behavior?

RealtimeClient gracefully falls back to alternative WebSocket implementations when isows is unavailable:
• Uses window.WebSocket in browser environments
• Uses global.WebSocket if globally available
• Falls back to Node.js ws package
• Maintains optimal performance by preferring isows when available

Additional context

• All existing tests pass, ensuring no regressions.
• Checked against this test PR
• Maintains backward compatibility - existing code continues to work unchanged
• No breaking changes to the public API