Summary

Implement BGSAVE, BGSAVE SCHEDULE, and BGSAVE CANCEL commands for both standalone and cluster clients, matching PHPRedis API and the implementation in other GLIDE clients (Go, Python,
Node, C#).

Issue link

This Pull Request is linked to issue (URL): #236
Related issues and pull requests:

• [2.5] Implement New Missing Commands [2.5] Implement New Missing Commands valkey-glide#6010
• feat: Add BGSAVE commands feat: Add BGSAVE commands valkey-glide-csharp#436

Features / Behaviour Changes

• Add ValkeyGlide::bgSave(?string $mode = null): bool|string for standalone client
• Add ValkeyGlideCluster::bgSave(mixed $route, ?string $mode = null): bool|string for cluster client
• PHPRedis compatible: Returns true on success, false on failure by default
• With OPT_REPLY_LITERAL enabled, returns the actual status string (e.g., "Background saving started")
• Supports three modes:
  • null (default): Initiates a background save immediately
  • "SCHEDULE": Schedules a background save
  • "CANCEL": Aborts in-progress/scheduled saves (Valkey 8.1+)

Implementation

• execute_bgsave_command() added in valkey_glide_commands.c
• BGSAVE_METHOD_IMPL macro added in valkey_glide_commands_common.h
• Macro invoked for ValkeyGlide in valkey_z_php_methods.c
• Macro invoked for ValkeyGlideCluster in valkey_glide_cluster.c
• BgSave case added to prepare_message_args switch in valkey_glide_core_common.c
• Added Map response type handling in process_core_string_result for cluster multi-node responses
• Stub definitions added to valkey_glide.stub.php and valkey_glide_cluster.stub.php

Testing

• 3 standalone tests: testBgSave, testBgSaveSchedule, testBgSaveCancel
• 3 cluster tests with route parameter
• BGSAVE CANCEL tests version-gated to Valkey 8.1+
• waitForSaveNotInProgress() helper prevents test conflicts from concurrent saves
• Verified OPT_REPLY_LITERAL returns actual string response

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.