Inline equals in StringIndex probe; drop the eq() guard helper

The `a == b || a.equals(b)` guard is a wash when equals inlines (benchmark: a
monomorphic String receiver lets equals's own leading `this == b` provide the
identity fast-path). And the eq() helper was an extra call in the hot probe,
consuming inline depth/budget; inlining `.equals()` directly flattens
indexOf -> equals, making equals more likely to inline -- the regime where the
guard is moot anyway.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dougqh

internal-api/src/main/java/datadog/trace/util/StringIndex.java

@@ -223,7 +223,7 @@ public static int put(int[] hashes, String[] names, String name, int h) {
           names[i] = name;
           return i;
         }
-        if (hashes[i] == h && eq(names[i], name)) {
+        if (hashes[i] == h && names[i].equals(name)) {
           return i; // already present
         }
       }
@@ -239,7 +239,7 @@ public static int indexOf(int[] hashes, String[] names, String name, int h) {
         if (sh == 0) {
           return -1;
         }
-        if (sh == h && eq(names[i], name)) {
+        if (sh == h && names[i].equals(name)) {
           return i;
         }
       }
@@ -288,10 +288,5 @@ public static long lookupOrDefault(
       int slot = indexOf(hashes, names, key);
       return slot >= 0 ? data[slot] : defaultValue;
     }
-
-    // `a` is a stored name on an occupied slot (never null); `b` is a non-null query.
-    private static boolean eq(String a, String b) {
-      return a == b || a.equals(b); // interned literals hit the == fast path
-    }
   }
 }