Add context handling to DerivAPI client

[ksysoev]

This pull request adds context handling to the DerivAPI client. It includes the following changes:

• Adds context to the API client struct

• Adds context handling in the request sender and response handler functions

• Adds a cancel function to the DerivAPI struct

• Updates the Connect and Disconnect functions to use the cancel function

• Updates the requestSender and handleResponses functions to check for context cancellation

• Updates the requestMapper function to check for context cancellation

• Adds a check for context cancellation in the SendRequest function

These changes improve the handling of context in the DerivAPI client, ensuring that requests can be cancelled when necessary.