Add show_wire_loops option to suppress cable self-loop edges

Cable self-loop edges (W1:e → W1:w) arc over the cable table to show
internal wire routing, but add visual noise on straight-through
harnesses. New Options field defaults to True for backward compat.

Usage:
  options:
    show_wire_loops: false

src/wireviz/wv_dataclasses.py

@@ -86,6 +86,7 @@ class Options:
     bgcolor_bundle: SingleColor = None
     color_output_mode: ColorOutputMode = ColorOutputMode.EN_UPPER
     mini_bom_mode: bool = True
+    show_wire_loops: bool = True
     template_separator: str = "."
     output_dpi: Optional[float] = 96.0
     _pad: int = 0

src/wireviz/wv_harness.py

@@ -387,9 +387,10 @@ class Harness:
                 if not (r1, r2) == (None, None):
                     dot.edge(r1, r2)
 
-            for color, we,  ww in gv_edge_wire_inside(cable):
-                if not (we,  ww) == (None, None):
-                    dot.edge(we,  ww, color=color, straight="straight", href='')
+            if self.options.show_wire_loops:
+                for color, we,  ww in gv_edge_wire_inside(cable):
+                    if not (we,  ww) == (None, None):
+                        dot.edge(we,  ww, color=color, straight="straight", href='')
         for mate in self.mates:
             color, dir, code_from, code_to = gv_edge_mate(mate)