These diagnostics occurred, but weren't treated as errors:
```
[WARN] Missing return type: alphablend on line 38
[WARN] Missing argument type: dest_bitmap on line 38
[WARN] Missing argument type: source_bitmap_1 on line 38
[WARN] Missing argument type: source_bitmap_2 on line 38
```
This object has a finalizer, so once it's no longer referenced, GC can
call that finalizer and then deallocate the storage.
In the case of a failure during construction (e.g., when checking
`validate_obj_is_free_pin_or_none`) this will happen on an incompletely
initialized structure. On samd, in particular, a newly allocated object
(with construct never called) appears to be valid, so GC collecting it
causes deinit() to do things, leading to a hard fault.
The double creation of the UART object was necessary specifically so that
the second allocation would fail. Probably there were other (single
call) ways to make it fail, but this was the easiest / the one discovered
in real life.
Closes: #5493
This targets the 64-bit CPU Raspberry Pis. The BCM2711 on the Pi 4
and the BCM2837 on the Pi 3 and Zero 2W. There are 64-bit fixes
outside of the ports directory for it.
There are a couple other cleanups that were incidental:
* Use const mcu_pin_obj_t instead of omitting the const. The structs
themselves are const because they are in ROM.
* Use PTR <-> OBJ conversions in more places. They were found when
mp_obj_t was set to an integer type rather than pointer.
* Optimize submodule checkout because the Pi submodules are heavy
and unnecessary for the vast majority of builds.
Fixes#4314
mp_obj_float_get gets the value of an object, which must be
exactly a float. mp_obj_get_float gets the float value of
an object of various types, including floats & ints.
