added j / k for vim-style line movement

j and k move the caret one line, delegated to sublime's own `move` command
so they behave exactly like the arrow keys. They dispatch through the
existing ACTIONS registry, so the keymap, the status-bar hints and the ?
popup all stay in sync through the single KEY_GROUPS table.

Unlike the other letter keys, j / k keep no command_mode context: the view
is read-only, so leaving them live while Vintage is in command mode can
only ever move the caret. That asymmetry was previously documented only in
a comment, which was wrong (it claimed j / k were the only unguarded
bindings, but escape has always carried its own context instead). It is now
pinned by test_command_mode_guard_is_deliberate, so normalising the keymap
fails the suite with the reason attached.

Also tidies two long lines in commands.py.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test_commands.py

@@ -135,3 +135,13 @@ def test_run_async_reports_generic_error(monkeypatch):
 
     commands.run_async(boom, lambda r: messages.append("done"))
     assert messages == ["vDiff: boom"]
+
+
+def test_j_and_k_move_the_caret_one_line():
+    view = sublime.View()
+    commands.ACTIONS["line_down"](view, None, None)
+    commands.ACTIONS["line_up"](view, None, None)
+    assert view.commands == [
+        ("move", {"by": "lines", "forward": True}),
+        ("move", {"by": "lines", "forward": False}),
+    ]