veb integration example

This example is a compile-time, in-memory veb.Context lifecycle sample. It does not start a veb server and does not bind a port.

The example is intentionally small because robust server lifecycle validation belongs to veb itself. Here, x.async only coordinates a synthetic handler step and returns the response body through Task.wait().

Run from the repository root:

./v run vlib/x/async/examples/veb/app_lifecycle.v