Add verification script

Merge and a few final tweaks

Merged main to fork

A crash like the following occurs in the unix port:
```
Program received signal SIGSEGV, Segmentation fault.
0x00005555555a2d7a in mp_obj_module_set_globals (self_in=0x55555562c860 <ulab_user_cmodule>, globals=0x55555562c840 <mp_module_ulab_globals>) at ../../py/objmodule.c:145
145	    self->globals = globals;
(gdb) up
#1  0x00005555555b2781 in mp_builtin___import__ (n_args=5, args=0x7fffffffdbb0) at ../../py/builtinimport.c:496
496	                mp_obj_module_set_globals(outer_module_obj,
(gdb)
adafruit#2  0x00005555555940c9 in mp_import_name (name=824, fromlist=0x555555621f10 <mp_const_none_obj>, level=0x1) at ../../py/runtime.c:1392
1392	    return mp_builtin___import__(5, args);
```

I don't understand how it doesn't happen on the embedded ports, because
the module object should reside in ROM and the assignment of self->globals
should trigger a Hard Fault.

By checking VERIFY_PTR, we know that the pointed-to data is on the heap
so we can do things like mutate it.

Um s2 boards

It was incorrect to NULL out the pointer to our heap allocated buffer in
`reset`, because subsequent to framebuffer_reset, but while
the heap was still active, we could call `get_bufinfo` again,
leading to a fresh allocation on the heap that is about to be destroyed.

Typical stack trace:
```
#1  0x0006c368 in sharpdisplay_framebuffer_get_bufinfo
adafruit#2  0x0006ad6e in _refresh_display
adafruit#3  0x0006b168 in framebufferio_framebufferdisplay_background
adafruit#4  0x00069d22 in displayio_background
adafruit#5  0x00045496 in supervisor_background_tasks
adafruit#6  0x000446e8 in background_callback_run_all
adafruit#7  0x00045546 in supervisor_run_background_tasks_if_tick
adafruit#8  0x0005b042 in common_hal_neopixel_write
adafruit#9  0x00044c4c in clear_temp_status
adafruit#10 0x000497de in spi_flash_flush_keep_cache
adafruit#11 0x00049a66 in supervisor_external_flash_flush
adafruit#12 0x00044b22 in supervisor_flash_flush
adafruit#13 0x0004490e in filesystem_flush
adafruit#14 0x00043e18 in cleanup_after_vm
adafruit#15 0x0004414c in run_repl
adafruit#16 0x000441ce in main
```
When this happened -- which was inconsistent -- the display would keep
some heap allocation across reset which is exactly what we need to avoid.

NULLing the pointer in reconstruct follows what RGBMatrix does, and that
code is a bit more battle-tested anyway.

If I had a motivation for structuring the SharpMemory code differently,
I can no longer recall it.

Testing performed: Ran my complicated calculator program over multiple
iterations without observing signs of heap corruption.

Closes: adafruit#3473