fix: Prevent DivisionByZeroError in BaseHandler::reproportion() with float 0.0

[gr8man]

Description
This PR fixes a potential DivisionByZeroError inside BaseHandler::reproportion() when processing image resizing operations where dimensions (origWidth or origHeight) might evaluate to 0.0 (float) or when provided dimensions are invalid.

Previously, the strict comparison check === 0 on float 0.0 allowed the execution to pass through the initial guard clause, causing a crash during proportion calculations.

Changes:

• Refactored reproportion() to safely cast inputs to int and centralize dimension validation.
• Added strict checks via is_numeric() to ensure both provided and original dimensions are mathematically valid.
• Introduced testReproportionWithFloatZero in BaseHandlerTest utilizing Reflection to directly test the protected method's early return behavior without side effects.

Checklist:

• Securely signed commits
• Component(s) with PHPdoc fully completed
• Unit testing, with >80% coverage
• User guide updated (if applicable)

[michalsn]

is_numeric() is much broader than ctype_digit(). 0.0 should be checked explicitly.

[michalsn]

Please use one of the ReflectionHelper methods instead: https://github.com/codeigniter4/CodeIgniter4/blob/develop/system/Test/ReflectionHelper.php

[michalsn]

I should have checked this earlier, but it looks like the PHPDoc for Image::$origWidth and Image::$origHeight is too broad. These values are populated from getimagesize(), and PHP implementation reads image dimensions as integer values: https://github.com/php/php-src/blob/master/ext/standard/image.c

Since getimagesize() returns integer width and height values, Image::$origWidth and Image::$origHeight should probably be documented as int rather than float|int. I don't think we should add defensive 0.0 handling to reproportion().