fix(tests): handle tmux version differences in options tests

Based on examination of tmux source code:

1. terminal-overrides defaults:
   - tmux 3.0a-3.1b: Have default values (xterm*, screen*)
   - tmux 3.2+: Defaults removed (commit 527f66ed, April 2020)

2. terminal-overrides parsing:
   - Fix split("=") to split("=", 1) to handle values containing "="
   - Example: "RGB=\E[...=%p1%d...]" was failing to parse

3. Style option behavior:
   - When bg=default is set, tmux stores bg as color 8 (default)
   - When converting to string, color 8 is omitted from output
   - Test was incorrectly expecting "bg=default" in output
   - This behavior is consistent across all tmux versions

References:
- /home/d/study/c/tmux-3.0a/options-table.c:219-223
- /home/d/study/c/tmux-3.2a/options-table.c:314-318
- /home/d/study/c/tmux-3.0a/style.c:174-245
- /home/d/study/c/tmux-3.2a/style.c:189-270

Author: tony

src/libtmux/options.py

@@ -510,7 +510,7 @@ def explode_complex(
                         if term not in new_overrides:
                             new_overrides[term] = {}
                         if features and "=" in features:
-                            k, v = features.split("=")
+                            k, v = features.split("=", 1)
 
                             if v.isdigit():
                                 v = int(v)

tests/test_options.py

@@ -489,12 +489,16 @@ def test_stable_baseline_options_and_hooks(server: Server) -> None:
             assert terminal_features["rxvt*"] == ["ignorefkeys"]
 
     # Terminal overrides differ by version
-    # In tmux 3.5+, terminal-overrides has a default value
-    if has_gte_version("3.5"):
+    # tmux 3.0a-3.1b: has default values (xterm*, screen*)
+    # tmux 3.2+: defaults removed, returns None unless explicitly set
+    if has_gte_version("3.2"):
         terminal_overrides = server.show_option("terminal-overrides")
         assert isinstance(terminal_overrides, (dict, type(None)))
     elif has_gte_version("3.0"):
-        assert server.show_option("terminal-overrides") is None
+        # tmux 3.0a/3.1b have defaults like "xterm*:XT:Ms=...,screen*:XT"
+        terminal_overrides = server.show_option("terminal-overrides")
+        assert isinstance(terminal_overrides, dict)
+        assert "screen*" in terminal_overrides or "xterm*" in terminal_overrides
     else:
         terminal_overrides = server.show_option("terminal-overrides")
         assert isinstance(terminal_overrides, dict)
@@ -573,12 +577,14 @@ def test_style_option_validation(server: Server) -> None:
     session = server.new_session(session_name="test")
 
     # Valid style (format differs between tmux versions)
+    # Note: when you set bg=default, tmux internally sets bg to 8 (default color)
+    # and when converting to string, it omits the bg property entirely
     session.set_option("status-style", "fg=red,bg=default,bold")
     style = session.show_option("status-style")
     assert isinstance(style, str)
     assert "fg=red" in str(style)
+    # bg=default is NOT included in output (tmux omits it when bg is default)
     if has_gte_version("3.0"):
-        assert "bg=default" in str(style)
         assert "bold" in str(style)
     else:
         assert "bright" in str(style)