Move our preload hacks out of keyboard_config into their own module. Isolate the ugliness

kmk/preload_imports.py

@@ -0,0 +1,45 @@
+# Welcome to RAM and stack size hacks central, I'm your host, klardotsh!
+# Our import structure is deeply nested enough that stuff
+# breaks in some truly bizarre ways, including:
+# - explicit RuntimeError exceptions, complaining that our
+#   stack depth is too deep
+#
+# - silent hard locks of the device (basically unrecoverable without
+#   UF2 flash if done in main.py, fixable with a reboot if done
+#   in REPL)
+#
+# However, there's a hackaround that works for us! Because sys.modules
+# caches everything it sees (and future imports will use that cached
+# copy of the module), let's take this opportunity _way_ up the import
+# chain to import _every single thing_ KMK eventually uses in a normal
+# workflow, in nesting order
+#
+# GC runs automatically after CircuitPython imports.
+
+# First, system-provided deps
+import busio
+import collections
+import gc
+import supervisor
+
+# Now "light" KMK stuff with few/no external deps
+import kmk.consts  # isort:skip
+import kmk.kmktime  # isort:skip
+import kmk.types  # isort:skip
+
+from kmk.consts import LeaderMode, UnicodeMode, KMK_RELEASE  # isort:skip
+from kmk.hid import USB_HID  # isort:skip
+from kmk.internal_state import InternalState  # isort:skip
+from kmk.keys import KC  # isort:skip
+from kmk.matrix import MatrixScanner  # isort:skip
+
+# Now handlers that will be used in keys later
+import kmk.handlers.layers  # isort:skip
+import kmk.handlers.stock  # isort:skip
+
+# Now stuff that depends on the above (and so on)
+import kmk.keys  # isort:skip
+import kmk.matrix  # isort:skip
+
+import kmk.hid  # isort:skip
+import kmk.internal_state  # isort:skip