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/feature_check/int_64.py

@@ -0,0 +1,2 @@
+# Check whether 64-bit long integers are supported
+print(1 << 62)

tests/feature_check/int_64.py.exp

@@ -0,0 +1 @@
+4611686018427387904