Fix websocket cookbook examples busy-looping after client disconnect

[wakqasahmed]

Both websocket cookbook examples (`cookbook/websocket/gorilla` and `cookbook/websocket/net`) run their write/read loop unconditionally — on a write or read error they log it and loop right back around instead of exiting. Once a client disconnects, every subsequent `WriteMessage`/`ReadMessage` call errors immediately, so the handler spins as fast as possible logging errors forever instead of returning.

Added an early return on both the write-error and read-error paths in each example, so the handler exits (and `defer ws.Close()` runs) as soon as the connection is gone, matching how these examples are meant to demonstrate correct websocket handling.

Added a test per example that connects a client, closes it immediately, and asserts the handler goroutine actually returns within a couple seconds — this fails against the old code (the handler never returns, so the test would time out) and passes with the fix.