feat(pycardium): Add micropython-lib, enable string

.gitmodules

 [submodule "lib/micropython/micropython"]
 	path = lib/micropython/micropython
 	url = https://github.com/micropython/micropython.git
+[submodule "lib/micropython/micropython-lib"]
+	path = lib/micropython/micropython-lib
+	url = https://github.com/micropython/micropython-lib.git

micropython-lib @ b89114c8

+Subproject commit b89114c8345e15d360c3707493450805c114bc8c

pycardium/modules/py/meson.build

 python_modules = files(
   'color.py',
   'htmlcolor.py',
+  'string.py',
 )
 
 frozen_modules = mpy_cross.process(python_modules)

pycardium/modules/py/string.py

+../../../lib/micropython/micropython-lib/string/string.py
\ No newline at end of file