tests: Add specific tests for "long long" 64-bit bigints.

These will run on all ports which support them, but importantly
they'll also run on ports that don't support arbitrary precision
but do support 64-bit long ints.

Includes some test workarounds to account for things which will overflow
once "long long" big integers overflow (added in follow-up commit):

- uctypes_array_load_store test was failing already, now won't parse.
- all the ffi_int tests contain 64-bit unsigned values, that won't parse
  as long long.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

tests/extmod/uctypes_array_load_store.py

@@ -6,6 +6,13 @@ except ImportError:
     print("SKIP")
     raise SystemExit
 
+# 'int' needs to be able to represent UINT64 for this test
+try:
+    int("FF" * 8, 16)
+except OverflowError:
+    print("SKIP")
+    raise SystemExit
+
 N = 5
 
 for endian in ("NATIVE", "LITTLE_ENDIAN", "BIG_ENDIAN"):