Add Redis JSON module support

[imperugo]

Summary

Add support for the Redis JSON module (RedisJSON) for native server-side JSON operations with JSONPath queries.

Why

Redis JSON allows storing, querying, and manipulating JSON documents directly on the server without full deserialization — critical for large documents where you only need a few fields.

Key Operations

• `JSON.SET` / `JSON.GET` — store/retrieve JSON
• `JSON.MGET` — multi-key JSON get
• `JSON.NUMINCRBY` — atomic numeric increment within JSON
• `JSON.ARRAPPEND` — append to JSON array
• `JSON.DEL` — delete JSON path
• `JSON.TYPE` — get type at path

Considerations

• Requires Redis Stack (not vanilla Redis)
• SE.Redis may not have native typed API — may need `ExecuteAsync` with raw commands
• Consider a separate NuGet package: `StackExchange.Redis.Extensions.Json`
• JSONPath query support is the differentiating feature