fix: make stub cache directory configurable via env

[vyacheslavdanilin]

Summary
This PR makes the stub cache directory location configurable via an environment variable LARAVEL_PLUGIN_CACHE_PATH.

Details
Previously, the path to the cache directory was hardcoded. This change allows overriding the default location by setting the LARAVEL_PLUGIN_CACHE_PATH environment variable, which is particularly useful when using Psalm in different CI or Docker environments.

Example Usage

export LARAVEL_PLUGIN_CACHE_PATH=/tmp/custom-laravel-psalm-cache ./vendor/bin/psalm 

or in Dockerfile / CI pipeline:

env: LARAVEL_PLUGIN_CACHE_PATH: /tmp/cache 

Closes: #361

[Copilot]

Pull Request Overview

This PR enables configuring the stub cache directory via the environment variable LARAVEL_PLUGIN_CACHE_PATH, allowing customized cache locations in CI and Docker environments.

• Makes cache directory configurable via an environment variable
• Updates the CacheDirectoryProvider to trim trailing slashes if the environment variable is set
• Adds unit tests validating both default and custom cache paths

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/Unit/Providers/CacheDirectoryProviderTest.php	Adds tests to verify default path and custom env-variable paths
src/Providers/CacheDirectoryProvider.php	Updates provider to return the trimmed env-path if set

Comments suppressed due to low confidence (1)

src/Providers/CacheDirectoryProvider.php:19

• [nitpick] The default cache path concatenation uses a hardcoded '/'. Consider using DIRECTORY_SEPARATOR to improve compatibility across different operating systems.

return __DIR__ . '/../../cache'; 

[alies-dev]

Looks great! I just only have a concern about the name: LARAVEL_PLUGIN_CACHE_PATH doesn't contain any mentions about PSALM, that in some configs may be confusing people ("what type pf plugin?"). WDTY?

[vyacheslavdanilin]

Renamed to PSALM_LARAVEL_PLUGIN_CACHE_PATH as suggested — thanks!