adds stream disconnect handler for streaming calls

[akshaydeo]

Improved Stream Cancellation Handling for Client Disconnects

This PR adds proper handling of client disconnections during streaming operations across all providers. When a client disconnects mid-stream, the system now properly cleans up resources and updates log status from "processing" to "error" with a 499 status code.

Changes

• Added HandleStreamCancellation utility function in providers/utils to standardize client disconnect handling
• Implemented context cancellation checks in all provider streaming implementations
• Added deferred cleanup handlers that detect context cancellation and trigger proper error reporting
• Added context checks before processing each stream chunk to exit early when clients disconnect
• Fixed request type tracking for proper cleanup in OpenAI's responses-to-chat fallback mode

Type of change

• Bug fix
• Feature

Affected areas

• Core (Go)
• Providers/Integrations

How to test

1. Start a streaming request with any provider
2. Disconnect the client mid-stream (close browser tab, terminate connection)
3. Verify logs show proper error status with 499 code
4. Check that resources are properly released

# Core/Transports
go test ./core/providers/...

Breaking changes

• No

Security considerations

This change improves resource management by ensuring proper cleanup when clients disconnect unexpectedly, preventing potential resource leaks.

Checklist

• I added/updated tests where appropriate
• I verified builds succeed (Go and UI)