fix(vegas): a display duration that is not a number no longer cancels a static pause

The Vegas static pause compared plugin.get_display_duration() with the
clock. clock-simple, calendar and countdown return their display_duration
setting straight from config.json, so a value saved as "20" or null
reached that comparison as a string or None. The TypeError went to the
pause's broad except, which ended the pause: the plugin flashed up and
the scroll went straight on, at every one of its turns. inf held the
pause until something interrupted it, and NaN, False, 0 or a negative
number ended it at once.

The pause now reads the duration the way the rotation has since #739,
with the same helper, then the rotation's fallbacks: 30 s for anything
that is not a number or a get_display_duration() that raises, 15 s for a
number at or below zero. Logged once per plugin. test_vegas_static_mode.py's
pauses used 0 to mean "no wait"; they now use 0.01.

The helper moves from display_controller (_finite_seconds) to base_plugin
(finite_seconds), unchanged: the coordinator cannot import from
display_controller, which imports src.vegas_mode at module level, and a
new src module would turn ledmatrix-plugins' min-core table check red
until it was listed. base_plugin is already loaded whenever either one is.

Tests: test/test_vegas_static_pause_duration.py, on a fake clock,
including TestSameAsTheRotation, which runs every value through both the
pause and the rotation's _get_display_duration/_resolve_durations.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/test_vegas_static_mode.py

@@ -219,7 +219,8 @@ class TestCoordinatorStaticPause:
     def _plugin(self):
         plugin = MagicMock()
         plugin.plugin_id = 'clock'
-        plugin.get_display_duration.return_value = 0
+        # A moment: zero would pause 15 s, as the rotation shows it.
+        plugin.get_display_duration.return_value = 0.01
         return plugin
 
     def test_trigger_comes_from_the_pipeline(self):