py/parsenum: Use int instead of mp_int_t for parsing float exponent.
py/parsenum: Use int instead of mp_int_t for parsing float exponent.

There is no need to use the mp_int_t type which may be 64-bits wide, there
is enough bit-width in a normal int to parse reasonable exponents.  Using
int helps to reduce code size for 64-bit ports, especially nan-boxing
builds.  (Similarly for the "dig" variable which is now an unsigned int.)

selste/micropython,bvernoux/micropython,bvernoux/micropython,kerneltask/micropython,adafruit/micropython,tobbad/micropython,tobbad/micropython,henriknelson/micropython,henriknelson/micropython,henriknelson/micropython,bvernoux/micropython,MrSurly/micropython,tralamazza/micropython,pramasoul/micropython,pramasoul/micropython,tralamazza/micropython,pfalcon/micropython,trezor/micropython,trezor/micropython,pozetroninc/micropython,selste/micropython,pfalcon/micropython,selste/micropython,pfalcon/micropython,tralamazza/micropython,trezor/micropython,pfalcon/micropython,adafruit/circuitpython,swegener/micropython,swegener/micropython,bvernoux/micropython,tobbad/micropython,pramasoul/micropython,kerneltask/micropython,selste/micropython,dmazzella/micropython,tobbad/micropython,adafruit/circuitpython,swegener/micropython,kerneltask/micropython,pozetroninc/micropython,swegener/micropython,adafruit/micropython,MrSurly/micropython,pozetroninc/micropython,selste/micropython,dmazzella/micropython,bvernoux/micropython,pozetroninc/micropython,adafruit/circuitpython,pramasoul/micropython,dmazzella/micropython,henriknelson/micropython,tobbad/micropython,MrSurly/micropython,adafruit/circuitpython,MrSurly/micropython,swegener/micropython,kerneltask/micropython,trezor/micropython,pozetroninc/micropython,kerneltask/micropython,pfalcon/micropython,adafruit/micropython,MrSurly/micropython,adafruit/circuitpython,dmazzella/micropython,adafruit/micropython,trezor/micropython,henriknelson/micropython,adafruit/circuitpython,pramasoul/micropython,adafruit/micropython,tralamazza/micropython