Implement IHybridCache adapter (.NET 9+)

[imperugo]

Summary

Implement Microsoft.Extensions.Caching.Hybrid.HybridCache backed by StackExchange.Redis.Extensions.

What is HybridCache

HybridCache (.NET 9+) combines L1 (in-memory) and L2 (distributed) caching with stampede protection. It's the recommended caching abstraction going forward, replacing IDistributedCache for most scenarios.

Proposed Integration

services.AddStackExchangeRedisExtensions<SystemTextJsonSerializer>(config);
services.AddRedisHybridCache(); // registers HybridCache with Redis as L2

Considerations

• Requires .NET 9+ (net9.0/net10.0 TFMs only)
• Needs `IDistributedCache` as a prerequisite (Implement IDistributedCache adapter #632)
• Stampede protection is built into HybridCache — we just need the L2 backend
• Serialization should use our `ISerializer` for consistency