refactor(adapter)!: drop the valkey adapter in favor of redis

Valkey speaks the Redis protocol, so the redis adapter (go-redis) already
serves it. Dropping valkey-go removes a dependency and shrinks the stripped
binary by about 9 MB.

The redis adapter now also closes a client that failed to connect only once.

BREAKING CHANGE: `adapter: valkey` is no longer accepted. Use
`adapter: redis` with a redis:// or rediss:// URL instead of valkey:// or
valkeys://. The namespace option now applies to these services.

go.mod

@@ -7,7 +7,6 @@ require (
 	github.com/go-sql-driver/mysql v1.10.0
 	github.com/lib/pq v1.12.3
 	github.com/redis/go-redis/v9 v9.19.0
-	github.com/valkey-io/valkey-go v1.0.75
 	go.mongodb.org/mongo-driver/v2 v2.6.0
 	gopkg.in/yaml.v3 v3.0.1
 )