hooks(feat): add warning for set_hooks on tmux < 3.0

why: Hook arrays are a tmux 3.0+ feature. On tmux < 3.0, hooks are
stored by exact name in a red-black tree, so "session-renamed[0]"
is a literal hook name, not an array index. This causes unexpected
behavior with set_hooks and clear_existing.

what:
- Add UserWarning when set_hooks is called on tmux < 3.0
- Warning explains the limitation and references tmux commit dfb7bb68

Ref: tmux commit dfb7bb68 (April 2019) merged hooks into options
as array options for tmux 3.0.

Author: tony

src/libtmux/hooks.py

@@ -483,6 +483,18 @@ def set_hooks(
         >>> session.unset_hook('after-new-window')  # doctest: +SKIP
         Session($...)
         """
+        # Hook arrays require tmux 3.0+. On older versions, hooks are stored
+        # by exact name (e.g. "session-renamed[0]" is a literal name, not an
+        # array index). See tmux commit dfb7bb68 (April 2019).
+        if has_lt_version("3.0"):
+            warnings.warn(
+                "Hook arrays require tmux 3.0+. "
+                "On older versions, set_hooks creates hooks with literal bracket "
+                "names (e.g. 'session-renamed[0]') instead of array indices, "
+                "and clear_existing/unset_hook may not work as expected.",
+                stacklevel=2,
+            )
+
         if clear_existing:
             self.unset_hook(hook, global_=global_, scope=scope)