v0.1.0

test(bench): cover the handshake and timer handlers (#136)

Adds benchmarks for `initiate_handshake`, `handle_handshake_initiation`,
`handle_handshake_response`, `handle_cookie_reply`, `poll_timeout` and
`handle_timeout` (both with nothing due and with a keepalive due). Like
the data path's `begin_*` and `commit_*` steps, these run on the thread
that owns the tunnel, so their cost bounds a single tunnel's handshake
and timer throughput.

Co-authored-by: Claude <noreply@anthropic.com>