is_manifold() and is_valid discrepancy()

[CasperH2O]

As requested by @gumyr on Discord. Version 0.8.0 of b123d

The following code results in is_manifold stating true, while is_valid states false.

import build123d
from build123d import *
from ocp_vscode import *

length_width = 40.0

with BuildPart() as hook_part:
    with BuildLine() as hook:
        line_1 = Polyline([(0,20.0),(20.0,20.0),(20.0,0)])
    with BuildSketch(line_1 ^ 0) as b3:
        Rectangle(length_width,length_width)
    sweep(transition=Transition.ROUND)

show_object(hook_part)

print(f"\n{build123d.__version__}")
print(f"Amount of faces: {len(hook_part.part.faces())}")
print(f"is_valid: {hook_part.part.is_valid()}")
print(f"is_manifold: {hook_part.part.is_manifold}") # Holds water?

Terminal output:

Using port 3939 taken from config file
Jupyter console not installed
+
0.8.0
Amount of faces: 14
is_valid: False
is_manifold: True