feat: add readonly flags to schemas

Previously, TypeScript allowed you to modify schema objects at the
typing level, but this modification caused errors because the schema
objects themselves were frozen at the JavaScript level. This commit
adds readonly flags for schemas to fix the problem above.

Author: dmitrytavern

types/property.d.ts

@@ -88,7 +88,7 @@ export type PropertySchema<
   E extends PropertyElementType = any,
   R extends PropertyRequired = any,
   D extends PropertyDefault<T, E> = any
-> = Required<PropertySchemaTemplate<T, E, R, D>>
+> = Readonly<Required<PropertySchemaTemplate<T, E, R, D>>>
 
 /**
  * For creating the `PropertySchema` object you need to pass some options

types/schema.d.ts

@@ -44,14 +44,16 @@ import {
  * @public
  */
 export type Schema<SRaw extends RawSchema = any> =
-  SRaw extends RawSchemaAsObject ? SchemaAsObject<SRaw> : SchemaAsAnyObject
+  SRaw extends RawSchemaAsObject
+    ? Readonly<SchemaAsObject<SRaw>>
+    : Readonly<SchemaAsAnyObject>
 
 type SchemaAsObject<SRaw extends RawSchemaAsObject> = {
-  [P in keyof SRaw]: SchemaTypeProperty<SRaw[P]>
+  readonly [P in keyof SRaw]: SchemaTypeProperty<SRaw[P]>
 }
 
 type SchemaAsAnyObject = {
-  [key: string]: Schema | PropertySchema
+  readonly [key: string]: Schema | PropertySchema
 }
 
 type SchemaTypeProperty<P> = P extends PropertyTypeRaw
@@ -132,7 +134,7 @@ export type RawSchemaProperty =
  * @public
  */
 export type SchemaReturn<S extends Schema = any> = {
-  [P in keyof S]: SchemaReturnProperty<S[P]>
+  -readonly [P in keyof S]: SchemaReturnProperty<S[P]>
 }
 
 type SchemaReturnProperty<P extends Schema | PropertySchema | PropertyTypeRaw> =