Pane,Window(fix[respawn]): use fused -c flag format for consistency

why: The pane/window split() and new_window() methods use the fused
form (f"-c{path}",) for the start-directory flag. The respawn methods
used the separated form ("-c", str(path)), diverging from the dominant
pattern in pane/window code.
what:
- Change Pane.respawn -c from ("-c", str(start_path)) to (f"-c{start_path}",)
- Change Window.respawn -c from ("-c", str(start_path)) to (f"-c{start_path}",)

Author: tony

src/libtmux/pane.py

@@ -1703,7 +1703,7 @@ def respawn(
 
         if start_directory is not None:
             start_path = pathlib.Path(start_directory).expanduser()
-            tmux_args += ("-c", str(start_path))
+            tmux_args += (f"-c{start_path}",)
 
         if environment:
             for k, v in environment.items():

src/libtmux/window.py

@@ -761,7 +761,7 @@ def respawn(
 
         if start_directory is not None:
             start_path = pathlib.Path(start_directory).expanduser()
-            tmux_args += ("-c", str(start_path))
+            tmux_args += (f"-c{start_path}",)
 
         if environment:
             for k, v in environment.items():