feat: add PHP 8.5 support

Summary

The current composer.json restricts PHP to 8.1 - 8.4, which explicitly excludes PHP 8.5+.

Background

This constraint was introduced in PR #156 (merged 2025-07-25) when PHP 8.4 support was added. At that time, the CI matrix was updated to include 8.4, and the version range was narrowed to match the tested versions — which is a reasonable practice. However, PHP 8.5 has since been released, and the constraint has not been updated.

Analysis

After reviewing the codebase, there are no known PHP 8.5 incompatibilities in this package. The restriction appears to be purely declarative (CI has not been run against 8.5 yet), rather than a technical limitation.

Request

Please consider:

1. Adding 8.5 to the CI test matrix (GitHub Actions)
2. Updating composer.json to extend the PHP constraint to 8.1 - 8.5

Context

We are running a Yii3 project that targets PHP 8.5 (~8.5.0). This package is currently installable only with --ignore-platform-req=php, which is a workaround we'd like to avoid. All other yiisoft/* packages in our stack already declare 8.1 - 8.5 support.

Thank you for maintaining this package!

Start by reviewing composer.json and the GitHub Actions CI configuration, especially the existing PHP version matrix. Run the current CI checks with PHP 8.5 and confirm the package dependency constraint accepts it. Done means PHP 8.5 is tested in CI and declared as supported without requiring --ignore-platform-req=php.