fix(bar): use truncated labels for titles

This commit introduces a new wrapper, CustomUi, which is used to
implement custom methods on top of eframe::egui::Ui.

The default ui::add_sized method always has the text in a label
centered, which is not desirable for a status bar where the layout
should be ltr.

A new function CustomUi::add_sized_left_to_right has been added to
ensure that labels can be truncated with a custom width (which requires
allocate_ui_with_layout), while also retaining the ability for the text
to be aligned to the left rather than the center of the allocated
layout.

schema.bar.json

@@ -408,6 +408,11 @@
         ]
       }
     },
+    "max_label_width": {
+      "description": "Max label width before text truncation (default: 400.0)",
+      "type": "number",
+      "format": "float"
+    },
     "monitor": {
       "description": "Monitor options",
       "type": "object",