py/objarray: Raise error on out-of-bound memoryview slice start.

32-bit platforms only support a slice offset start of 24 bit max due to the
limited size of the mp_obj_array_t.free member.  Similarly on 64-bit
platforms the limit is 56 bits.

This commit adds an OverflowError if the user attempts to slice a
memoryview beyond this limit.

Signed-off-by: Damien George <damien@micropython.org>

tests/basics/memoryview_slice_size.py

@@ -0,0 +1,27 @@
+# test memoryview slicing beyond the limit of what memoryview can internally index
+
+try:
+    from sys import maxsize
+    from uctypes import bytearray_at
+
+    memoryview
+except:
+    print("SKIP")
+    raise SystemExit
+
+if maxsize <= 0xFFFF_FFFF:
+    slice_max = 0xFF_FFFF
+else:
+    slice_max = 0xFF_FFFF_FFFF_FFFF
+
+buf = bytearray_at(0, slice_max + 2)
+mv = memoryview(buf)
+
+# this should work
+print(mv[slice_max : slice_max + 1])
+
+# this should overflow the internal index for memoryview slicing
+try:
+    print(mv[slice_max + 1 : slice_max + 2])
+except OverflowError:
+    print("OverflowError")

tests/basics/memoryview_slice_size.py.exp

@@ -0,0 +1,2 @@
+<memoryview>
+OverflowError