Exclude attributes from Endpoint.toString() (#6061)

Motivation:

We observed `OutOfMemoryError` in internal CI tests when a new
`Endpoint` is created.
```
com.linecorp.armeria.xds.client.endpoint.EndpointsPool$$Lambda$754/1708334230@3a58f44e
    java.lang.OutOfMemoryError: Java heap space
        at java.util.Arrays.copyOfRange(Arrays.java:3664)
        at java.lang.String.<init>(String.java:207)
        at java.lang.StringBuilder.toString(StringBuilder.java:412)
        at com.google.protobuf.TextFormat$Printer.printToString(TextFormat.java:593)
        at com.google.protobuf.AbstractMessage.toString(AbstractMessage.java:87)
        at java.lang.String.valueOf(String.java:2994)
        at java.lang.StringBuilder.append(StringBuilder.java:136)
        at com.linecorp.armeria.internal.shaded.guava.collect.AbstractMapEntry.toString(AbstractMapEntry.java:70)
        at java.lang.String.valueOf(String.java:2994)
        at java.lang.StringBuilder.append(StringBuilder.java:136)
        at com.linecorp.armeria.internal.shaded.guava.collect.Iterators.toString(Iterators.java:294)
        at com.linecorp.armeria.common.ImmutableAttributes.toString(ImmutableAttributes.java:183)
        at java.lang.String.valueOf(String.java:2994)
        at java.lang.StringBuilder.append(StringBuilder.java:136)
        at com.linecorp.armeria.client.Endpoint.generateToString(Endpoint.java:304)
        at com.linecorp.armeria.client.Endpoint.<init>(Endpoint.java:268)
        at com.linecorp.armeria.client.Endpoint.replaceAttrs(Endpoint.java:747)
        at com.linecorp.armeria.client.Endpoint.withAttr(Endpoint.java:707)
        at com.linecorp.armeria.xds.client.endpoint.EndpointsPool.withTimestamp(EndpointsPool.java:103)
        at com.linecorp.armeria.xds.client.endpoint.EndpointsPool.cacheAttributesAndDelegate(EndpointsPool.java:71)
        at com.linecorp.armeria.xds.client.endpoint.EndpointsPool.lambda$updateClusterSnapshot$1(EndpointsPool.java:62)
        at com.linecorp.armeria.xds.client.endpoint.EndpointsPool$$Lambda$754/1708334230.run(Unknown Source)
```
When an `Endpoint` is initicated, it pre-generates a string
representation for caching and reuse. In our tests, it contained many
attributes related to xDS for service discovery. It might be a good idea
to remove attributes whose size is hard to predict from `toString()` and
prevent unintended OOM.

In addition, the result size of `toString()` gets small, so I doubt that
the pre-generated cache is useful for performance.

Modifications:

- Remove attributes from `toString()`.
- Lazily build the string representation when `toString()` is called and
don't cache the result.

Result:

`Endpoint` no longer includes attributes in `.toString()`.

core/src/main/java/com/linecorp/armeria/client/Endpoint.java

@@ -232,7 +232,6 @@ enum Type {
     private final int weight;
     private final List<Endpoint> endpoints;
     private final String authority;
-    private final String strVal;
 
     @Nullable
     private final Attributes attributes;
@@ -264,8 +263,6 @@ private Endpoint(Type type, String host, @Nullable String ipAddr, int port, int
 
         // Pre-generate the authority.
         authority = generateAuthority(type, host, port);
-        // Pre-generate toString() value.
-        strVal = generateToString(type, authority, ipAddr, weight, attributes);
         this.attributes = attributes;
     }
 
@@ -291,22 +288,6 @@ private static String generateAuthority(Type type, String host, int port) {
         }
     }
 
-    private static String generateToString(Type type, String authority, @Nullable String ipAddr,
-                                           int weight, @Nullable Attributes attributes) {
-        try (TemporaryThreadLocals tempThreadLocals = TemporaryThreadLocals.acquire()) {
-            final StringBuilder buf = tempThreadLocals.stringBuilder();
-            buf.append("Endpoint{").append(authority);
-            if (type == Type.HOSTNAME_AND_IP) {
-                buf.append(", ipAddr=").append(ipAddr);
-            }
-            buf.append(", weight=").append(weight);
-            if (attributes != null) {
-                buf.append(", attributes=").append(attributes);
-            }
-            return buf.append('}').toString();
-        }
-    }
-
     @Override
     public List<Endpoint> endpoints() {
         return endpoints;
@@ -981,6 +962,14 @@ public int compareTo(Endpoint that) {
 
     @Override
     public String toString() {
-        return strVal;
+        try (TemporaryThreadLocals tempThreadLocals = TemporaryThreadLocals.acquire()) {
+            final StringBuilder buf = tempThreadLocals.stringBuilder();
+            buf.append("Endpoint{").append(authority);
+            if (type == Type.HOSTNAME_AND_IP) {
+                buf.append(", ipAddr=").append(ipAddr);
+            }
+            return buf.append(", weight=").append(weight)
+                      .append('}').toString();
+        }
     }
 }

core/src/test/java/com/linecorp/armeria/client/EndpointTest.java

@@ -539,8 +539,9 @@ void testToString() {
 
         // attributes
         final Endpoint endpointWithAttr = Endpoint.of("127.0.0.1").withAttr(AttributeKey.valueOf("test"), 1);
+        // toString() should not include the attributes.
         assertThat(endpointWithAttr.toString())
-                .isEqualTo("Endpoint{127.0.0.1, weight=1000, attributes=[test=1]}");
+                .isEqualTo("Endpoint{127.0.0.1, weight=1000}");
     }
 
     @Test