countio: add selectable rise and fall detection, pulls

[dhalbert]

• Addresses countio enhancements #5606.

• Add selectable counting of rising or falling edges, or both (both is not possible on RP2040).

• Add ability to specify a pull-up or pull-down.

• The default was supposed to be falling, though on RP2040 it appears to have been rising. Fixed RP2040 to be consistent.

• Renamed pin argument of Counter() to be pin instead of pin_a. Not sure why it was pin_a. That may be a leftover of something else.

• Remove common_hal_countio_counter_reset(), since it can be done by common_hal_countio_counter_set_count(pin, 0).

• Introduce countio.Edge enumeration. The alternative was to provide rise and fall boolean arguments to Counter(), but seems more consistent with other such multi-value arguments.

• Unrelated: Fix some kind of accidental typo for the symbolic link for tests/pyboard.py -> ../tools/cpboard.py. The symoblic link included a literal newline character, which is not obvious from the file comparison below.

Tested on all the implemented platforms: raspberrypi, espressif, atmel-samd, nrf:

• Pulls tested manually.
• Slight variants of this test program used on different boards:

import board
import time
from countio import Counter, Edge
from digitalio import DigitalInOut

tx = DigitalInOut(board.TX)
tx.switch_to_output(False)

a0 = Counter(board.A0, edge=Edge.RISE)
a2 = Counter(board.A2, edge=Edge.FALL)
a4 = Counter(board.A4, edge=Edge.RISE_AND_FALL)

while True:
    print(f"tx: {tx.value}, a0 (rise): {a0.count}, a2 (fall): {a2.count}, a4 (r/f): {a4.count}")
    tx.value = not tx.value
    time.sleep(1)

[jepler]

Not tested, but did read through the changes. Looks good from here.