docs(gax-grpc): add comment explaining resize delta clamping in staticallySized

Author: lqiu96

sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/ChannelPoolSettings.java

@@ -139,6 +139,9 @@ public static ChannelPoolSettings staticallySized(int size) {
         .setMaxRpcsPerChannel(Integer.MAX_VALUE)
         .setMinChannelCount(size)
         .setMaxChannelCount(size)
+        // Maintain backwards compatibility by using default delta (2).
+        // For static size 1, clamp to avoid validation failure (delta <= max channels).
+        // Since static pools don't resize, this value doesn't affect operation.
         .setMaxResizeDelta(Math.min(DEFAULT_MAX_RESIZE_DELTA, size))
         .build();
   }