Mark namespace classes as final with private constructors

src/main/java/com/garciat/typeclasses/TypeClasses.java

@@ -10,7 +10,9 @@
 import java.util.Arrays;
 import java.util.List;
 
-public class TypeClasses {
+public final class TypeClasses {
+  private TypeClasses() {}
+
   public static <T> T witness(Ty<T> ty, Ctx<?>... context) {
     return switch (WitnessSummoning.summon(ParsedType.parse(ty.type()), parseContext(context))) {
       case Either.Left<SummonError, Object>(SummonError error) ->

src/main/java/com/garciat/typeclasses/impl/ConstructorLookup.java

@@ -10,7 +10,9 @@
 import java.util.Arrays;
 import java.util.List;
 
-public class ConstructorLookup {
+public final class ConstructorLookup {
+  private ConstructorLookup() {}
+
   public static List<InstanceConstructor> findRules(ParsedType target) {
     return switch (target) {
       case ParsedType.App(var fun, var arg) -> Lists.concat(findRules(fun), findRules(arg));

src/main/java/com/garciat/typeclasses/impl/OverlappingInstances.java

@@ -6,7 +6,9 @@
 import com.garciat.typeclasses.impl.WitnessRule.InstanceConstructor;
 import java.util.List;
 
-public class OverlappingInstances {
+public final class OverlappingInstances {
+  private OverlappingInstances() {}
+
   /**
    * @implSpec <a href=
    *     "https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/instances.html#overlapping-instances">6.8.8.5.

src/main/java/com/garciat/typeclasses/impl/Unification.java

@@ -6,7 +6,9 @@
 import java.util.List;
 import java.util.Map;
 
-public class Unification {
+public final class Unification {
+  private Unification() {}
+
   public static Maybe<Map<ParsedType.Var, ParsedType>> unify(ParsedType t1, ParsedType t2) {
     return switch (Pair.of(t1, t2)) {
       case Pair<ParsedType, ParsedType>(ParsedType.Var var1, ParsedType.Primitive p) ->

src/main/java/com/garciat/typeclasses/impl/WitnessInstantiation.java

@@ -9,7 +9,9 @@
 import java.util.Map;
 import java.util.stream.Collectors;
 
-public class WitnessInstantiation {
+public final class WitnessInstantiation {
+  private WitnessInstantiation() {}
+
   /** Compiles an InstantiationPlan into an Expr. */
   public static Expr<ParsedType> compile(InstantiationPlan plan) {
     return switch (plan) {

src/main/java/com/garciat/typeclasses/impl/WitnessResolution.java

@@ -7,7 +7,9 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
-public class WitnessResolution {
+public final class WitnessResolution {
+  private WitnessResolution() {}
+
   /** Resolves a ParsedType into an InstantiationPlan. */
   public static Either<ResolutionError, InstantiationPlan> resolve(
       ParsedType target, List<ContextInstance> context) {

src/main/java/com/garciat/typeclasses/impl/WitnessSummoning.java

@@ -4,7 +4,9 @@
 import com.garciat.typeclasses.types.Either;
 import java.util.List;
 
-public class WitnessSummoning {
+public final class WitnessSummoning {
+  private WitnessSummoning() {}
+
   public static Either<SummonError, Object> summon(
       ParsedType target, List<ContextInstance> context) {
     return WitnessResolution.resolve(target, context)