Implement migrate command

[prateek-kumar-improving]

Summary

Implement the MIGRATE command for both standalone and cluster clients. Supports single-key migration (both clients), multi-key migration (standalone only), COPY/REPLACE flags, and AUTH/AUTH2 credentials.

Issue link

This Pull Request is linked to issue: #236
Linked issue: #275

Features / Behaviour Changes

• Add ValkeyGlide::migrate(string $host, int $port, string|array $key, int $dstdb, int $timeout, bool $copy = false, bool $replace = false, mixed $credentials = null): ValkeyGlide|bool|string
• Add ValkeyGlideCluster::migrate(...): same but single-key only
• PHPRedis compatible signature
• Returns true on success (OK/NOKEY), false on error
• With OPT_REPLY_LITERAL enabled, returns raw status string ("OK" or "NOKEY") on success, false on failure
• Cluster mode: single-key only (matching Java/Python/Go limitation)
• Supports COPY, REPLACE, AUTH, and AUTH2

Implementation

• execute_migrate_command() in valkey_glide_commands.c
• MIGRATE_METHOD_IMPL macro using STANDARD_METHOD_IMPL
• Migrate case added to prepare_message_args switch (alphabetized)
• Increased core_command_args_t.args from [8] to [12]
• Multi-key handled by iterating PHP array as individual STRING args
• Credentials support: string → AUTH, array [username, password] → AUTH2
• Test infrastructure: startDestinationServer()/stopDestinationServer() helpers using cluster_manager.py

Testing

Standalone tests (tests/ValkeyGlideTest.php) added.
Cluster tests (tests/ValkeyGlideClusterTest.php) added.
Build passes with -Werror, lint clean on all modified files.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one 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.

[currantw]

Reviewed to 2c1ce7d.

[currantw]

Reviewed to 6296505.

[Aryex]

lgtm

[currantw]

Reviewed to 100f017.

[currantw]

Just one remaining comment about possible duplicate tests

[currantw]

Reviewed to 8ce99a9.
Looks good ✅
Thanks @prateek-kumar-improving 🎉