Boxplot fix median line extending past box boundaries (matplotlib#26462)

Closes matplotlib#19409.

- Set the default capstyles (solid and dashed) for median and mean lines in boxplots to "butt".
  I also modieifed the behaviror for setting the capstyle for median lines to obey the user's preference
  instead of overriding it.
- The boxplot PDFs were using the wrong capstyle, so I modified the references to use the butt captyle.
- Fixed a small typo in `bxp()`
- Added a new test for the median line (from PR matplotlib#23335)

Co-authored-by: Elliott Sales de Andrade <[email protected]>

Author: kidkoder432

lib/matplotlib/axes/_axes.py

@@ -4095,7 +4095,7 @@ def bxp(self, bxpstats, positions=None, widths=None, vert=True,
 
         capwidths : float or array-like, default: None
           Either a scalar or a vector and sets the width of each cap.
-          The default is ``0.5*(with of the box)``, see *widths*.
+          The default is ``0.5*(width of the box)``, see *widths*.
 
         vert : bool, default: True
           If `True` (default), makes the boxes vertical.
@@ -4147,6 +4147,17 @@ def bxp(self, bxpstats, positions=None, widths=None, vert=True,
         --------
         .. plot:: gallery/statistics/bxp.py
         """
+        # Clamp median line to edge of box by default.
+        medianprops = {
+            "solid_capstyle": "butt",
+            "dash_capstyle": "butt",
+            **(medianprops or {}),
+        }
+        meanprops = {
+            "solid_capstyle": "butt",
+            "dash_capstyle": "butt",
+            **(meanprops or {}),
+        }
 
         # lists of artists to be output
         whiskers = []