PHP: add PHPRedis compatibility check script

[prateek-kumar-improving]

Summary

Adds a script (compatibility_check.php) that generates a compatibility report comparing the Valkey GLIDE PHP client against PHPRedis for both standalone (Redis vs ValkeyGlide) and
cluster (RedisCluster vs ValkeyGlideCluster) APIs.

Issue link

This Pull Request is linked to issue (URL): No issue

Features / Behaviour Changes

The script categorizes every PHPRedis command into four groups:

1. Compatible APIs — Implemented in Glide with matching PHPRedis signature
2. Not Compatible APIs — Present in both but with different argument signatures
3. Not Supported in Valkey — PHPRedis commands for features not in the Valkey engine (Redis 8+, KeyDB, vector sets)
4. Not Implemented — Commands supported by Valkey and present in PHPRedis, but not yet implemented in Glide

Outputs a summary to stdout and writes a detailed COMPATIBILITY_REPORT.md.

Current results

	Standalone	Cluster
Compatible	75.6%	83.3%
Not Compatible	4.3%	4.8%
Not Supported in Valkey	9.3%	3.5%
Not Implemented	10.9%	8.3%

How to run

bash
php compatibility_check.php

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one issue - No issue
• Commit message has a detailed description of what changed and why.
• Tests are added or updated.
• CHANGELOG.md and documentation files are updated.
• Destination branch is correct - main or release
• Create merge commit if merging release branch into main, squash otherwise.

[jamesx-improving]

LGTM. Two non-blocking comments for the author's consideration.