Generalize OTEL API and add memcache tracing support

- Rename RedisSpan -> SpanHandle for generic span handling
- Generalize TelemetryController methods: startSpan/endSpan with dbSystem param
- Rename RedisOtelSpan -> OtelSpanHandle in rbcs-server-otel
- Update Redis cache handler to use new generic API
- Add OpenTelemetry tracing for memcache GET and SET commands
- Add channel property to MemcacheRequestController for server address attribution
- Add uses TelemetryController directive in memcache module-info

Memcache spans follow the same pattern as Redis:
db.system=memcache, db.operation=GET|SET, server.address, server.port

rbcs-api/src/main/java/net/woggioni/rbcs/api/SpanHandle.java

@@ -2,7 +2,7 @@ package net.woggioni.rbcs.api;
 
 import org.jetbrains.annotations.NotNull;
 
-public interface RedisSpan {
+public interface SpanHandle {
 
     void setAttribute(@NotNull String key, @NotNull String value);
 

rbcs-api/src/main/java/net/woggioni/rbcs/api/TelemetryController.java

@@ -8,9 +8,9 @@ public interface TelemetryController {
     void initialize();
     @NotNull ChannelHandler createHandler();
 
-    @Nullable RedisSpan startRedisSpan(@NotNull String command, @NotNull String key);
+    @Nullable SpanHandle startSpan(@NotNull String command, @NotNull String key, @NotNull String dbSystem);
 
-    void endRedisSpan(@Nullable RedisSpan span);
+    void endSpan(@Nullable SpanHandle span);
 
-    void endRedisSpan(@Nullable RedisSpan span, @NotNull Throwable error);
+    void endSpan(@Nullable SpanHandle span, @NotNull Throwable error);
 }