String::toInt() and atol() behave different on different platforms with a number that is too large.

User axemaster found strange behavior when using String::toInt() with a number that is too large. See the topic in the Arduino forum: [https://forum.arduino.cc/t/toint-bug-how-unfortunate/1041669](https://forum.arduino.cc/t/toint-bug-how-unfortunate/1041669).
The result is different for 8-bit and 32-bit platforms.
It was narrowed down to the undefined behaviour of atol() when a number is too large to fit in a long.

The atol() in String::toInt() in String.cpp could be replaced by strtol() followed by a check for LONG_MAX or LONG_MIN and return zero if that happens. The documentation can stay as it is, because it will return a long, and zero if something is wrong.
To allow LONG_MAX and LONG_MIN as valid input numbers, the errno has to be used. I don't know how that will hold up in a multitasking environment.

Start in String.cpp at String::toInt() and review how atol() behaves for values outside the platform's long range. Compare the proposed strtol() and errno handling across 8-bit and 32-bit platforms; the issue is done when oversized inputs produce consistent documented results without mishandling LONG_MAX or LONG_MIN.

Written by the indexing model from the issue text.