fix: Buffer overflow in bytes_to_read

[BradleyKirton]

Hi there 👋

I encountered a runtime exception in invoke/terminals.py::bytes_to_read on Python 3.14.

I believe the issue is because the original version passed the incorrect sized arg to fcntl.ioctl.

gh-132915: [fcntl.fcntl()](https://docs.python.org/3/library/
fcntl.html#fcntl.fcntl) and fcntl.ioctl() can now detect a buffer overflow and raise SystemError. The stack and memory can be corrupted in such case, so treat this error as fatal.

See python/cpython#132915

I have created this PR which provides correctly sized arg.