Sketch close returns start point of for construction edge when closing non construction edge

`Sketch` `close()` closes an edge that is not for construction with an edge created with `forConstruction=True`.

I attempted to close the triangle with itself, however, it was closed with the starting point of the for construction arc.

```py
import cadquery as cq

s0 = (
cq.Sketch()
.arc((0, 0), 30, 0, 120, tag="e0", forConstruction=True)
.edges(tag="e0")
.distribute(1, rotate=False)
.segment((0, 0), (10, 2))
.segment((10, -2))
.close()
# .assemble()
)

show_object(s0, name="s0")
```


Uncommenting `assemble()`:


A solution is to omit close by explicitly specifying the edge end/start point:

```py
s0 = (
cq.Sketch()
.arc((0, 0), 30, 0, 120, tag="e0", forConstruction=True)
.edges(tag="e0")
.distribute(1, rotate=False)
.segment((0, 0), (10, 2))
.segment((10, -2))
.segment((0, 0))
.assemble()
)
```


Solution using callback:

```py
def triangle(loc):
s = cq.Sketch().segment((0, 0), (10, 2)).segment((10, -2)).close().assemble()
return s.moved(loc)

s0 = (
cq.Sketch()
.arc((0, 0), 30, 0, 120, tag="e0", forConstruction=True)
.edges(tag="e0")
.distribute(1, rotate=False)
.each(triangle)
)
```

Is there a scenario where it is desired to close an edge in non construction mode with an edge in construction mode?
If not, perhaps Sketch `_startPoint` can be changed to something like this:

```py
def _startPoint(self) -> Vector:

if not self._edges:
raise ValueError("No free edges available")

# find the first edge matching current edge mode
mode = self._edges[-1].forConstruction
for edge in reversed(self._edges):
if edge.forConstruction != mode:
break
prevedge = edge

e = prevedge

# current implementation selects first edge:
# e = self._edges[0]

return e.startPoint()
```

I didn't find any failing tests with this change.