Align the module on PrestaShop 8.2+ and bump to 4.0.0

[mattgoud]

Questions	Answers
Description?	Align the module on the PrestaShop 8.2+ floor set by the compatibility cleanup epic: ps_versions_compliancy min goes from 8.1.0 to 8.2.0, the PHPStan matrix drops the 8.1.7 core it no longer supports, and the module moves to 4.0.0. Also fixes the one PHPStan 2 finding that the develop matrix surfaced.
Type?	improvement
BC breaks?	yes
Deprecations?	no
Fixed ticket?	Part of PrestaShop/PrestaShop#41648
How to test?	CI: the PHPStan (PHP 7.4 - 8.1) job must now run twice (8.2.x x 7.4 and 8.2.x x 8.1) instead of four times, and every PHPStan job must be green. Functionally: on a PrestaShop 8.1 shop the module must be reported as incompatible, on 8.2 and above it installs and configures normally, the Module Manager must show version 4.0.0, and the home page slider must still render its slides with their sizes.
Sponsor company	@PrestaShopCorp

Why

The Modules - Cleaning Compatibility epic sets the floor at PS 8.2+. Nineteen of the twenty-two native modules raised during this campaign declare 8.2.0; three still declared 8.1.0, this module among them.

What changes

1. ps_versions_compliancy min 8.1.0 -> 8.2.0.
2. .github/workflows/php.yml: the phpstan-74 job matrix goes from presta_version: ['8.1.7', '8.2.x'] to ['8.2.x']. The php_version axis is untouched, so PHP 7.4 and 8.1 are still both covered.
3. tests/php/phpstan/phpstan-8.1.7.neon is deleted. The shared PrestaShop/.github PHPStan action interpolates matrix.presta_version into phpstan-config, so that file becomes unreachable the moment the matrix entry goes, and a leftover neon rots silently.
   Same for tests/php/phpstan/phpstan-latest.neon: no workflow has referenced a latest PrestaShop version since the matrix moved to explicit versions, and the file was a stale duplicate of the 9.x ones.
4. Module version 3.2.2 -> 4.0.0 in ps_imageslider.php and config.xml. The last published release is v3.2.2 and still declares min 1.7.5.0, so raising the floor to 8.2.0 is a breaking change for the shops that version supports, which makes the next release a major.
5. README.md: the compatibility line still announced 8.1.0, now 8.2.0.

The other four PHPStan jobs (9.0.3, 9.1.5, 9.2.x, develop) are unchanged.

The develop matrix turned red, and it is not this PR

PrestaShop develop moved from PHPStan 1.x to 2.x with PrestaShop/PrestaShop#42252, merged on 2026-09-04. The workflow runs ../../vendor/bin/phpstan, so the binary comes from the analysed branch. This module's dev was last analysed on 2026-08-31, four days before that bump, so this PR is simply its first run under PHPStan 2 and the finding predates it.

ps_imageslider.php:586 called is_array() on the return of getSlides(), which is the output of Db::executeS(), typed as an array by the php-dev-tools stub. The condition is therefore always true. The guard was also the only one of its kind in the file: getSlides() itself iterates its result directly at line 737, and so do its two other callers at lines 249 and 796. Removed rather than suppressed, consistent with how the same finding was handled in PrestaShop/ps_facetedsearch#1327.

Out of scope

The PHP support item of the epic is already satisfied here: the syntax check job covers 7.2 to 8.5. Unrelated to this PR, composer.json still declares an old php floor. That is a wider topic across native modules and is raised on the epic rather than fixed here.