feat: Support password update

[currantw]

Summary

This pull request implements dynamic password update functionality.

Key Changes

• Rust FFI: Added update_connection_password function.
• C# Bindings: Added FFI method declarations for both .NET 8+ and legacy frameworks.
• Public API: Added UpdateConnectionPasswordAsync and ClearConnectionPasswordAsync methods to BaseClient
• Integration Tests: Added comprehensive tests for both standalone and cluster clients

API Usage

// Update password without immediate authentication
await client.UpdateConnectionPasswordAsync("new_password");

// Update password with immediate authentication  
await client.UpdateConnectionPasswordAsync("new_password", immediateAuth: true);

// Remove password from connection
await client.ClearConnectionPasswordAsync();

Note: There is some variation in the dynamic password update interface between clients. In Java and Node, a single update method is provided; if the password is null or the empty string, the password is cleared. In Go, there is a separate method that "resets" the password. I chose to follow Go's approach, with two separate methods, because I think that it is more explicit. (Of course, I though that "clear" made the effects of the method *ahem* clearer than "reset").

[yipin-chen]

LGTM