`_remote_debugging`: `BinaryWriter.write_sample()` trivial segfault

Bug report

Bug description:

[139] 2026-09-09T18:57:09.249268000+0200 maurycy@gimel /Users/maurycy/work/cpython (main 52ffffe) % ./python.exe 
Python 3.16.0a0 (heads/main:83dbe6ae9f4, Sep  6 2026, 18:18:16) [Clang 21.0.0 (clang-2100.1.1.101)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import _remote_debugging
>>> _remote_debugging.BinaryWriter("/tmp/o.bin", 1000, 1000000).write_sample([42], 2000)
zsh: segmentation fault  ./python.exe

There's many more variants, easy to come up with.

This is the place:

https://github.com/python/cpython/blob/52ffffe0a23bf0f4a57ee00377c5aeb965b3a29a/Modules/_remote_debugging/binary_io_writer.c#L1013

It only checks if it's a list, and then it trusts completely:

https://github.com/python/cpython/blob/52ffffe0a23bf0f4a57ee00377c5aeb965b3a29a/Modules/_remote_debugging/binary_io_writer.c#L841-L848

https://github.com/python/cpython/blob/52ffffe0a23bf0f4a57ee00377c5aeb965b3a29a/Modules/_remote_debugging/binary_io_writer.c#L928-L930

https://github.com/python/cpython/blob/52ffffe0a23bf0f4a57ee00377c5aeb965b3a29a/Modules/_remote_debugging/binary_io_writer.c#L1020-L1023

The comment says Use unchecked accessors since we control the data structures but I still think that segmentation fault on a public method is not great.

I will submit a PR soon.

ref #148178

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-157228

Start in Modules/_remote_debugging/binary_io_writer.c at BinaryWriter.write_sample() and the referenced unchecked-accessor locations. Reproduce the crash with the provided BinaryWriter(...).write_sample([42], 2000) call, then verify that invalid public inputs no longer segfault and that the behavior is covered by appropriate regression testing.