sleep used without importing time.sleep in `_wait_for_legacy_endpoint`

[Karthik777]

def _wait_for_legacy_endpoint(self, timeout:float=5.0):
    if not isinstance(self.t, LegacySSETransport): return
    start = _now()
    while self.t._post_url is None and _now() - start < timeout: sleep(0.01)
    if self.t._post_url is None: raise MCPTransportError('Legacy SSE server did not send an endpoint event')

the sleep errors out with an import error