options(refactor[convert_values]): Remove dead SparseArray branch

why: The SparseArray-specific branch at lines 248-251 was unreachable
dead code. Since SparseArray inherits from dict, isinstance(value, dict)
returns True and the dict branch handles it correctly first.

what:
- Remove unreachable SparseArray branch that contained buggy logic
- Add comment explaining dict branch handles SparseArray too

Author: tony

src/libtmux/options.py

@@ -242,13 +242,10 @@ def convert_values(
     if value is None:
         return None
     if isinstance(value, dict):
+        # Note: SparseArray inherits from dict, so this branch handles both
         for k, v in value.items():
             value[k] = convert_value(v)
         return value
-    if isinstance(value, SparseArray):
-        for v in value.iter_values():
-            value[v] = convert_value(v)
-        return value
     if isinstance(value, list):
         for idx, v in enumerate(value):
             value[idx] = convert_value(v)