tmux_cmd(fix[logging]): Fix logging convention violations

why: f-string in logger.exception and .format() in post-exec log defeat lazy
formatting; shlex.join(cmd) was computed twice redundantly.
what:
- Compute shlex.join(cmd) once into cmd_str variable
- Replace f-string in logger.exception with lazy formatting + extra
- Replace .format() post-exec log with lazy formatting + structured extra
- Guard post-exec debug log with logger.isEnabledFor(logging.DEBUG)

Author: tony

src/libtmux/common.py

@@ -260,10 +260,11 @@ def __init__(self, *args: t.Any, tmux_bin: str | None = None) -> None:
 
         self.cmd = cmd
 
+        cmd_str = shlex.join(cmd)
         logger.debug(
             "running %s",
-            shlex.join(cmd),
-            extra={"tmux_cmd": shlex.join(cmd)},
+            cmd_str,
+            extra={"tmux_cmd": cmd_str},
         )
 
         try: