[Feature Request] Add clear_context() method to ClaudeSDKClient for context reset without reconnection

Problem

When using ClaudeSDKClient in a long-running/daemon process, there is no way to reset conversation context while keeping the connection alive. The only workaround is disconnect() + creating a new ClaudeSDKClient, which incurs 2-5 seconds startup overhead per request due to CLI subprocess initialization.

Proposed Solution

Add a clear_context() method that resets conversation history while keeping the connection alive:

async with ClaudeSDKClient(options=options) as client:
    await client.query("Task 1...")
    await collect_response(client)
    
    # Clear context, keep connection alive
    await client.clear_context()
    
    # Fresh context, no memory of Task 1
    await client.query("Task 2...")

Implementation Suggestion

Add a new control request subtype "clear_context" in the control protocol, similar to existing "interrupt", "set_model", etc:

{
  "type": "control_request",
  "request": { "subtype": "clear_context" }
}

Use Cases

1. API Gateway / Service Mode: A single long-running process handling multiple independent user requests
2. Batch Processing: Processing multiple unrelated tasks without context leakage
3. Multi-tenant Applications: Ensuring user A's data doesn't leak to user B

Current Workaround

# Slow: ~3-5 seconds per request due to CLI startup
for request in requests:
    async with ClaudeSDKClient(options=options) as client:
        await client.query(request)

Environment

• SDK Version: 0.1.33
• CLI Version: 2.1.37