Fix various Error Prone errors that were found by the FOSS build

Most common:
- Unnecessary parentheses and operator precedence clarify (self-explanatory)
- Reference equality--there were a few instances of using == or != improperly
- Qualification of Builder (and similar) imports so that it's clear which type of Builder we're referring to
- Marking some immutable classes with @Immutable since EP desires that all enums be deeply immutable
- String.split() having "surprising behavior"

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=230971531

java/google/registry/model/index/EppResourceIndexBucket.java

@@ -41,7 +41,7 @@ public class EppResourceIndexBucket extends ImmutableObject {
   private static long getBucketIdFromEppResource(Key<? extends EppResource> resourceKey) {
     int numBuckets = getEppResourceIndexBucketCount();
     // IDs can't be 0, so add 1 to the hash.
-    return Hashing.consistentHash(resourceKey.getName().hashCode(), numBuckets) + 1;
+    return Hashing.consistentHash(resourceKey.getName().hashCode(), numBuckets) + 1L;
   }
 
   /** Gets a bucket key as a function of an EppResource to be indexed. */