py/objint: Fix int.to_bytes() buffer size checks.

Fixes and improvements to `int.to_bytes()` are:
- No longer overflows if byte size is 0 (closes #13041).
- Raises OverflowError in any case where number won't fit into byte length
  (now matches CPython, previously MicroPython would return a truncated
  bytes object).
- Document that `micropython int.to_bytes()` doesn't implement the optional
  signed kwarg, but will behave as if `signed=True` when the integer is
  negative (this is the current behaviour).  Add tests for this also.

Requires changes for small ints, MPZ large ints, and "long long" large
ints.

Adds a new set of unit tests for ints between 32 and 64 bits to increase
coverage of "long long" large ints, which are otherwise untested.

Tested on unix port (64 bit small ints, MPZ long ints) and Zephyr STM32WB
board (32 bit small ints, long long large ints).

This work was funded through GitHub Sponsors.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/docs/library/builtins.rst b/docs/library/builtins.rst
index 7a0229c2a..e489375b1 100644
--- a/docs/library/builtins.rst
+++ b/docs/library/builtins.rst
@@ -82,6 +82,10 @@ Functions and types
       In MicroPython, `byteorder` parameter must be positional (this is
       compatible with CPython).
 
+      .. note:: The optional ``signed`` kwarg from CPython is not supported.
+                MicroPython currently converts negative integers as signed,
+                and positive as unsigned. (:ref:`Details <cpydiff_types_int_to_bytes>`.)
+
 .. function:: isinstance()
 
 .. function:: issubclass()