fix(pycardium): Implement proper delays

The old delay implementation is based on `mxc_delay`, provided by the
SDK.  This implementation has issues, as details in #177.  To fix these
issues, `mxc_delay` is replaced with a re-implementation which polls the
MicroPython scheduler and calls `wfi` when we can safely sleep.

The SysTick timer is configured globally (on core 1) to tick every 80ms.
This seems to be a reasonable value to allow at least some `wfi`-sleep
in the bounds used by most apps.

Signed-off-by: Rahix <rahix@rahix.de>