workspace/builder(fix[doctest]): Increase readiness doctest timeout to 5s

why: The 2s timeout was too tight for slow environments, causing
flaky doctest failures when the shell hadn't drawn its prompt yet.
what:
- Bump _wait_for_pane_ready doctest timeout from 2.0 to 5.0 seconds

Author: tony

src/tmuxp/workspace/builder.py

@@ -53,7 +53,7 @@ def _wait_for_pane_ready(
 
     Wait for the shell to be ready:
 
-    >>> _wait_for_pane_ready(pane, timeout=2.0)
+    >>> _wait_for_pane_ready(pane, timeout=5.0)
     True
     """
     start = time.monotonic()