sleep used without importing time.sleep in `_wait_for_legacy_endpoint`

```
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

Locate the `_wait_for_legacy_endpoint` entry point and inspect the surrounding imports. Reproduce the legacy endpoint wait that reaches `sleep(0.01)`, then run the relevant test suite. Done means this wait no longer raises the reported import error.

Written by the indexing model from the issue text.