Optimize ChunkProviderServer's chunk level checking helper methods

These can be hot functions (i.e entity ticking and block ticking),
so inline where possible, and avoid the abstraction of the
Either class.

Spigot-Server-Patches/Reduce-Either-Optional-allocation.patch

@@ -7,7 +7,7 @@ In order to get chunk values, we shouldn't need to create
 an optional each time.
 
 diff --git a/src/main/java/com/mojang/datafixers/util/Either.java b/src/main/java/com/mojang/datafixers/util/Either.java
-index a90adac7b..4bb621d57 100644
+index a90adac7b..3f65fe710 100644
 --- a/src/main/java/com/mojang/datafixers/util/Either.java
 +++ b/src/main/java/com/mojang/datafixers/util/Either.java
 @@ -0,0 +0,0 @@ public abstract class Either<L, R> implements App<Either.Mu<R>, L> {
@@ -15,20 +15,16 @@ index a90adac7b..4bb621d57 100644
  
      private static final class Left<L, R> extends Either<L, R> {
 -        private final L value;
-+        private final L value; private final Optional<L> valueOptional; // Paper - reduce the optional allocation...
++        private final L value; private Optional<L> valueOptional; // Paper - reduce the optional allocation...
  
          public Left(final L value) {
--            this.value = value;
-+            this.value = value; this.valueOptional = value != null ? Optional.of(value) : Optional.empty();  // Paper - reduce the optional allocation...
-         }
- 
-         @Override
+             this.value = value;
 @@ -0,0 +0,0 @@ public abstract class Either<L, R> implements App<Either.Mu<R>, L> {
  
          @Override
          public Optional<L> left() {
 -            return Optional.of(value);
-+            return this.valueOptional; // Paper - reduce the optional allocation...
++            return this.valueOptional == null ? this.valueOptional = Optional.of(this.value) : this.valueOptional; // Paper - reduce the optional allocation...
          }
  
          @Override
@@ -37,20 +33,16 @@ index a90adac7b..4bb621d57 100644
  
      private static final class Right<L, R> extends Either<L, R> {
 -        private final R value;
-+        private final R value; private final Optional<R> valueOptional; // Paper - reduce the optional allocation...
++        private final R value; private Optional<R> valueOptional; // Paper - reduce the optional allocation...
  
          public Right(final R value) {
--            this.value = value;
-+            this.value = value; this.valueOptional = value != null ? Optional.of(value) : Optional.empty(); // Paper - reduce the optional allocation...
-         }
- 
-         @Override
+             this.value = value;
 @@ -0,0 +0,0 @@ public abstract class Either<L, R> implements App<Either.Mu<R>, L> {
  
          @Override
          public Optional<R> right() {
 -            return Optional.of(value);
-+            return this.valueOptional; // Paper - reduce the optional allocation...
++            return this.valueOptional == null ? this.valueOptional = Optional.of(this.value) : this.valueOptional; // Paper - reduce the optional allocation...
          }
  
          @Override