Fix various small things

A commit that fixes all of the little things I forgot about, but that
are necessary for rendering to function properly.

- (attr. lines) reverse lines before extending above
- (attr. lines) clamp the AttributedLine offset so that there is always
  a line with offset 0
- (tree renderer) use meta spaces for the cursor too
- (tree renderer) use correct indent text for cursor
- (tree renderer) fix mypy error by safely ignoring it
- (supply) sort by root id instead of value
- (supply) return id, not list of ids

cheuph/attributed_lines.py

@@ -75,7 +75,7 @@ class AttributedLines:
         AttributedLines's offsets instead.
         """
 
-        self._lines.extendleft(lines._lines)
+        self._lines.extendleft(reversed(lines._lines))
         self.upper_offset -= len(lines)
 
     def extend_below(self, lines: "AttributedLines") -> None:
@@ -105,6 +105,7 @@ class AttributedLines:
 
         attr_lines = AttributedLines(lines)
         attr_lines.upper_offset = max(start_offset, self.upper_offset)
+        attr_lines.lower_offset = min(end_offset, self.lower_offset)
         return attr_lines
 
     def to_size(self, start_offset: int, end_offset: int) -> "AttributedLines":