forbidIncrementDecrementOnNonInteger: support BcMath\Number

[mpesari]

This adds support for BcMath\Number increment/decrement operators (on PHP >= 8.4)

php > $x = new BcMath\Number('3.14');
php > print $x;
3.14
php > $x++;
php > print $x;
4.14

As of phpstan 2.1.40, this is supported: https://phpstan.org/r/d2f000b7-4b86-45d4-9aba-7f0b302d7db5

However, these errors are emitted:

Using -- over non-integer (BcMath\Number)                               
         🪪  shipmonk.incrementDecrementOnNonInteger
etc...

I just added the required checks to ForbidIncrementDecrementOnNonIntegerRule, but...

• The rule name is weird after the changes. Would you prefer one of these instead:
  • Rename rule to something like ForbidIncrementDecrementOnUnsafeTypesRule?
  • Add parameter allowBcMathNumber?
• Would be nice to include tests for PHP < 8.4 too
  • What's the preferred way to achieve this? The simple way would be to use $this->analyse($files, $errors)

[janedbal]

Technically, even float++ is safe and somewhat valid, but we designed this rule to truely allow only integers in ++ and -- because we think that doing that over floats is mostly unintentional. You can always do + 1 for those. And since BcMath\Number is mainly designed to replace floats, I'd treat those the same way here.

[mpesari]

I understand. This extension produces the error:

Using ++ over non-integer (BcMath\Number)

There was some confusion due to phpstan-strict-rules' error:

Only numeric types are allowed in post-increment, BcMath\Number given.