Fix PHP 8.5 compatibility issues

[BridgelineTech]

This PR fixes several PHP 8.5 compatibility issues encountered while running Cacti Weathermap under PHP 8.5.

The changes address runtime TypeError failures caused by stricter parameter typing in PHP/GD, along with removal of imagedestroy() calls that are deprecated in PHP 8.5 but generate non-blocking log errors.

Changes include:

Cast numeric string values before passing them to round().
Ensure GD image coordinates and dimensions are integers where required.
Store and pass TrueType font sizes as floats.
Ensure find_distance() returns an integer array index.
Guard preg_match() so integer match references are not passed as the subject.
Cast legend coordinates before calling imagecopy().
Ensure thumbnail dimensions are integers.
Remove deprecated imagedestroy() calls. GD images have been GdImage objects since PHP 8.0 and are automatically released when no longer referenced.

These issues were encountered sequentially during actual Weathermap map generation on:

Cacti 1.2.30
PHP 8.5.4
Ubuntu 26.04

After applying these changes, the Weathermap poller successfully completes map generation without PHP 8.5 compatibility warnings or fatal errors:

SYSTEM WEATHERMAP STATS: Time:0.20 Maps:1 Warnings:0 Notes:None

The two separate EOF handling fixes are intentionally not included in this PR, as they have been submitted separately.

[TheWitness]

@BridgelineTech, can you please this wrapper around imagedestroy()? Otherwise, it looks good.

if (version_compare(PHP_VERSION, '8.5.0', '<')) {
   imagedestroy(blah);
}

[TheWitness]

Copilot is recommending the use of unset(blah) over imagedestry(bhah). That should be the fix I think.

[BridgelineTech]

Will do... I have a couple of additional fixes in my local for EOF and related that I have not yet submitted as PRs. I will try and get them all packaged up later, including the suggested "unset" vs just deleting. Thanks!