Convert function to constant

Avoid the disk access each time when this is checked. If users install
Terminus on the fly, they could restart ST to enable the commands.

plugin.py

@@ -169,9 +169,8 @@ class TestItemStatus(StrEnum):
 
 
 # Workaround until Terminus uses the Python 3.8 API environment
-def is_terminus_installed() -> bool:
- return os.path.isfile(os.path.join(INSTALLED_PACKAGES_PATH, 'Terminus.sublime-package')) or \
- os.path.isdir(os.path.join(PACKAGES_PATH, 'Terminus'))
+IS_TERMINUS_INSTALLED = os.path.isfile(os.path.join(INSTALLED_PACKAGES_PATH, 'Terminus.sublime-package')) or \
+ os.path.isdir(os.path.join(PACKAGES_PATH, 'Terminus'))
 
 
 def find_output_view(window: sublime.Window, name: str) -> sublime.View | None:
@@ -828,7 +827,7 @@ class JuliaOpenReplCommand(sublime_plugin.WindowCommand):
  def is_enabled(self) -> bool:
  # return importlib.find_loader("Terminus") is not None
  # Workaround until Terminus uses the Python 3.8 API environment
- return is_terminus_installed()
+ return IS_TERMINUS_INSTALLED
 
  def run(self, panel: bool = True) -> None:
  repl_view = find_output_view(self.window, JULIA_REPL_NAME)
@@ -878,7 +877,7 @@ def is_enabled(self, event: dict | None = None, point: int | None = None) -> boo
  # Terminus package must be installed
  # if not importlib.find_loader("Terminus"):
  # Workaround until Terminus uses the Python 3.8 API environment
- if not is_terminus_installed():
+ if not IS_TERMINUS_INSTALLED:
  return False
  # cursor must not be at end of file
  if self.view.sel()[0].b == self.view.size():
@@ -931,7 +930,7 @@ def is_enabled(self) -> bool:
  # Terminus package must be installed
  # if not importlib.find_loader("Terminus"):
  # Workaround until Terminus uses the Python 3.8 API environment
- if not is_terminus_installed():
+ if not IS_TERMINUS_INSTALLED:
  return False
  # cursor must not be at end of file
  if self.view.sel()[0].b == self.view.size():