ControlMode(env): Use split -e KEY=VAL args for new_window/split_window paths

why: Control mode ignores concatenated -eKEY=VAL when multiple env vars are passed; match tmux control expectations.
what:
- Emit env args as '-e', 'KEY=VAL' in Session.new_window and Pane.split
- Keep lint/format/type/tests green (regression suite unchanged)

Author: tony

src/libtmux/pane.py

@@ -688,7 +688,7 @@ def split(
         if environment:
             if has_gte_version("3.0"):
                 for k, v in environment.items():
-                    tmux_args += (f"-e{k}={v}",)
+                    tmux_args += ("-e", f"{k}={v}")
             else:
                 logger.warning(
                     "Environment flag ignored, tmux 3.0 or newer required.",

src/libtmux/server.py

@@ -690,7 +690,7 @@ def new_session(
         if environment:
             if has_gte_version("3.2"):
                 for k, v in environment.items():
-                    tmux_args += (f"-e{k}={v}",)
+                    tmux_args += ("-e", f"{k}={v}")
             else:
                 logger.warning(
                     "Environment flag ignored, tmux 3.2 or newer required.",

src/libtmux/session.py

@@ -691,7 +691,7 @@ def new_window(
         if environment:
             if has_gte_version("3.0"):
                 for k, v in environment.items():
-                    window_args += (f"-e{k}={v}",)
+                    window_args += ("-e", f"{k}={v}")
             else:
                 logger.warning(
                     "Environment flag ignored, requires tmux 3.0 or newer.",