Import and init cleanup

All imports made explicit
All redundant and unused imports removed
All circular import errors resolved

Imports alphabetized and sorted by source, in the following order: 
- Python Standard Library
- pip Packages
- Blender Libraries
- cam Modules (from .)

init split into multiple files:
New:
- cam_operation
- chain
- engine
- machine_settings
- preset_managers

Existing:
- pack
- slice
- ui
- utils

Rewrote get_panels to remove legacy panels and updated to follow Blender's guide: https://docs.blender.org/api/current/bpy.types.RenderEngine.html

scripts/addons/cam/async_op.py

@@ -1,8 +1,8 @@
-import bpy
 import sys
-
 import types
 
+import bpy
+
 
 @types.coroutine
 def progress_async(text, n=None, value_type='%'):

scripts/addons/cam/autoupdate.py

@@ -1,17 +1,18 @@
+import calendar
 from datetime import date
-from .version import __version__ as current_version
-from urllib.request import urlopen
+import io
 import json
+import os
 import pathlib
+import re
+import sys
+from urllib.request import urlopen
 import zipfile
+
 import bpy
 from bpy.props import StringProperty
 
-import re
-import io
-import os
-import sys
-import calendar
+from .version import __version__ as current_version
 
 
 class UpdateChecker(bpy.types.Operator):

scripts/addons/cam/basrelief.py

@@ -1,9 +1,14 @@
-import bpy
+from math import (
+    ceil,
+    floor,
+    sqrt
+)
+import re
 import time
+
 import numpy
-import math
-import re
-from math import *
+
+import bpy
 from bpy.props import (
     BoolProperty,
     EnumProperty,

scripts/addons/cam/bridges.py

@@ -19,21 +19,22 @@
 #
 # ***** END GPL LICENCE BLOCK *****
 # here is the bridges functionality of Blender CAM. The functions here are called with operators defined from ops.py.
+from math import (
+    hypot,
+    pi,
+)
+
+from shapely import ops as sops
+from shapely import geometry as sgeometry
+from shapely import prepared
 
 import bpy
-from bpy_extras.object_utils import AddObjectHelper, object_data_add
+from bpy_extras.object_utils import object_data_add
+from mathutils import Vector
 
 from . import utils
 from . import simple
 
-import mathutils
-import math
-
-
-from shapely import ops as sops
-from shapely import geometry as sgeometry
-from shapely import affinity, prepared
-
 
 def addBridge(x, y, rot, sizex, sizey):
     bpy.ops.mesh.primitive_plane_add(size=sizey*2, calc_uvs=True, enter_editmode=False, align='WORLD',
@@ -77,12 +78,12 @@ def addAutoBridges(o):
             minx, miny, maxx, maxy = c.bounds
             d1 = c.project(sgeometry.Point(maxx + 1000, (maxy + miny) / 2.0))
             p = c.interpolate(d1)
-            bo = addBridge(p.x, p.y, -math.pi / 2, o.bridges_width, o.cutter_diameter * 1)
+            bo = addBridge(p.x, p.y, -pi / 2, o.bridges_width, o.cutter_diameter * 1)
             g.objects.link(bo)
             bpy.context.collection.objects.unlink(bo)
             d1 = c.project(sgeometry.Point(minx - 1000, (maxy + miny) / 2.0))
             p = c.interpolate(d1)
-            bo = addBridge(p.x, p.y, math.pi / 2, o.bridges_width, o.cutter_diameter * 1)
+            bo = addBridge(p.x, p.y, pi / 2, o.bridges_width, o.cutter_diameter * 1)
             g.objects.link(bo)
             bpy.context.collection.objects.unlink(bo)
             d1 = c.project(sgeometry.Point((minx + maxx) / 2.0, maxy + 1000))
@@ -92,7 +93,7 @@ def addAutoBridges(o):
             bpy.context.collection.objects.unlink(bo)
             d1 = c.project(sgeometry.Point((minx + maxx) / 2.0, miny - 1000))
             p = c.interpolate(d1)
-            bo = addBridge(p.x, p.y, math.pi, o.bridges_width, o.cutter_diameter * 1)
+            bo = addBridge(p.x, p.y, pi, o.bridges_width, o.cutter_diameter * 1)
             g.objects.link(bo)
             bpy.context.collection.objects.unlink(bo)
 
@@ -153,8 +154,8 @@ def useBridges(ch, o):
             if vi + 1 < len(ch_points):
                 i2 = vi + 1
                 chp2 = ch_points[vi + 1]  # Vector(ch_points[vi+1])
-            v1 = mathutils.Vector(chp1)
-            v2 = mathutils.Vector(chp2)
+            v1 = Vector(chp1)
+            v2 = Vector(chp2)
             if v1.z < bridgeheight or v2.z < bridgeheight:
                 v = v2 - v1
                 p2 = sgeometry.Point(chp2)
@@ -181,13 +182,13 @@ def useBridges(ch, o):
                     newpoints.append((chp1[0], chp1[1], max(chp1[2], bridgeheight)))
                 cpoints = []
                 if itpoint:
-                    pt = mathutils.Vector((intersections.x, intersections.y, intersections.z))
+                    pt = Vector((intersections.x, intersections.y, intersections.z))
                     cpoints = [pt]
 
                 elif itmpoint:
                     cpoints = []
                     for p in intersections.geoms:
-                        pt = mathutils.Vector((p.x, p.y, p.z))
+                        pt = Vector((p.x, p.y, p.z))
                         cpoints.append(pt)
                 # ####sort collisions here :(
                 ncpoints = []
@@ -243,7 +244,7 @@ def useBridges(ch, o):
         if z == bridgeheight:   # find all points with z = bridge height
             count += 1
             if isedge == 1:     # This is to subdivide  edges which are longer than the width of the bridge
-                edgelength = math.hypot(x - x2, y - y2)
+                edgelength = hypot(x - x2, y - y2)
                 if edgelength > o.bridges_width:
                     # make new vertex
                     verts.append(((x + x2)/2, (y + y2)/2, o.minz))