bazel: Load java rules from @rules_java instead of built-ins

Bazel 8 and 9 continue the effort to "unbundle" language rules from
Bazel core. Loading java_binary and java_library from the internal
namespace is deprecated and disabled per default in Bezel 9 and will
be removed in Bazel 10.

This change explicitly loads these rules from @rules_java to ensure
compatibility with future Bazel versions and to follow modern best
practices.

Change-Id: I48002ede54240cd92c576af38fe113f3c3735a98

BUILD

diff --git a/BUILD b/BUILD
index 3879c4a..b759c02 100644
--- a/BUILD
+++ b/BUILD
@@ -1,3 +1,5 @@
+load("@rules_java//java:defs.bzl", "java_binary", "java_library")
+
 java_library(
     name = "java-prettify",
     srcs = glob(["src/**/*.java"]),