Add OpenTelemetry tracing support for Redis commands

- Add RedisSpan interface in rbcs-api for opaque span handles
- Extend TelemetryController with startRedisSpan/endRedisSpan methods
- Implement Redis tracing in rbcs-server-otel via OtelController and RedisOtelSpan
- Instrument RedisCacheHandler to create spans around GET and SET commands
- Add uses directive in rbcs-server-redis module-info for ServiceLoader discovery

Redis spans are created as CLIENT spans with attributes:
db.system=redis, db.operation=GET|SET, server.address, server.port

rbcs-server-redis/src/main/java/module-info.java

@@ -1,4 +1,5 @@
 import net.woggioni.rbcs.api.CacheProvider;
+import net.woggioni.rbcs.api.TelemetryController;
 
 module net.woggioni.rbcs.server.redis {
     requires net.woggioni.rbcs.common;
@@ -16,5 +17,7 @@ module net.woggioni.rbcs.server.redis {
 
     provides CacheProvider with net.woggioni.rbcs.server.redis.RedisCacheProvider;
 
+    uses TelemetryController;
+
     opens net.woggioni.rbcs.server.redis.schema;
 }