button: Add muted style to stream prefix.

The previous commits enables the ability to change style of button
prefix as well using prefix_markup. This makes the whole button
look muted.

Tests updated.

Author: Rohitth007

tests/ui_tools/test_buttons.py

@@ -195,6 +195,7 @@ def test_mark_muted(
 
         stream_button.mark_muted()
 
+        assert stream_button.prefix_style == "muted"
         assert stream_button.label_style == "muted"
         assert stream_button.suffix_style == "muted"
         assert stream_button.suffix_text == MUTE_MARKER
@@ -209,6 +210,7 @@ def test_mark_unmuted(
 
         stream_button.mark_unmuted(unread_count)
 
+        assert stream_button.prefix_style == stream_button.color
         assert stream_button.label_style is None
         assert stream_button.suffix_style == "unread_count"
         update_count.assert_called_once_with(unread_count)

zulipterminal/ui_tools/buttons.py

@@ -221,13 +221,15 @@ def __init__(
             self.mark_muted()
 
     def mark_muted(self) -> None:
+        self.prefix_style = "muted"
         self.label_style = "muted"
         self.suffix_style = "muted"
         self.suffix_text = MUTE_MARKER
         self.update_widget()
         self.view.home_button.update_count(self.model.unread_counts["all_msg"])
 
     def mark_unmuted(self, unread_count: int) -> None:
+        self.prefix_style = self.color
         self.label_style = None
         self.suffix_style = "unread_count"
         self.update_count(unread_count)