Improve == and hash methods on various schema cache structs to be allocation free.

The previous implementation would allocate 2 arrays per comparisons.

I tried relying on Struct, but they do allocate one Hash inside `Struct#hash`.

activerecord/lib/active_record/connection_adapters/column.rb

@@ -63,19 +63,24 @@ def encode_with(coder)
 
       def ==(other)
         other.is_a?(Column) &&
-          attributes_for_hash == other.attributes_for_hash
+          name == other.name &&
+          default == other.default &&
+          sql_type_metadata == other.sql_type_metadata &&
+          null == other.null &&
+          default_function == other.default_function &&
+          collation == other.collation
       end
       alias :eql? :==
 
       def hash
-        attributes_for_hash.hash
+        Column.hash ^
+          name.hash ^
+          default.hash ^
+          sql_type_metadata.hash ^
+          null.hash ^
+          default_function.hash ^
+          collation.hash
       end
-
-      protected
-
-        def attributes_for_hash
-          [self.class, name, default, sql_type_metadata, null, default_function, collation, comment]
-        end
     end
 
     class NullColumn < Column

activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb

@@ -16,19 +16,16 @@ def initialize(type_metadata, extra: "")
 
         def ==(other)
           other.is_a?(MySQL::TypeMetadata) &&
-            attributes_for_hash == other.attributes_for_hash
+            __getobj__ == other.__getobj__ &&
+            extra == other.extra
         end
         alias eql? ==
 
         def hash
-          attributes_for_hash.hash
+          TypeMetadata.hash ^
+            __getobj__.hash ^
+            extra.hash
         end
-
-        protected
-
-          def attributes_for_hash
-            [self.class, @type_metadata, extra]
-          end
       end
     end
   end

activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb

@@ -22,19 +22,20 @@ def sql_type
 
       def ==(other)
         other.is_a?(PostgreSQLTypeMetadata) &&
-          attributes_for_hash == other.attributes_for_hash
+          __getobj__ == other.__getobj__ &&
+          oid == other.oid &&
+          fmod == other.fmod &&
+          array == other.array
       end
       alias eql? ==
 
       def hash
-        attributes_for_hash.hash
+        PostgreSQLTypeMetadata.hash ^
+          __getobj__.hash ^
+          oid.hash ^
+          fmod.hash ^
+          array.hash
       end
-
-      protected
-
-        def attributes_for_hash
-          [self.class, @type_metadata, oid, fmod]
-        end
     end
   end
 end

activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb

@@ -16,19 +16,22 @@ def initialize(sql_type: nil, type: nil, limit: nil, precision: nil, scale: nil)
 
       def ==(other)
         other.is_a?(SqlTypeMetadata) &&
-          attributes_for_hash == other.attributes_for_hash
+          sql_type == other.sql_type &&
+          type == other.type &&
+          limit == other.limit &&
+          precision == other.precision &&
+          scale == other.scale
       end
       alias eql? ==
 
       def hash
-        attributes_for_hash.hash
+        SqlTypeMetadata.hash ^
+          sql_type.hash ^
+          type.hash ^
+          limit.hash ^
+          precision.hash >> 1 ^
+          scale.hash >> 2
       end
-
-      protected
-
-        def attributes_for_hash
-          [self.class, sql_type, type, limit, precision, scale]
-        end
     end
   end
 end