✨ feat!: v2 — strongly typed decorators on the TC39 standard

BREAKING CHANGE: cereale moves from legacy `experimentalDecorators` to TC39
standard decorators, which is what makes validation rules type-checked against
the fields they are attached to.

    class User {
      @IsString() name!: string;   // fine
      @IsString() age!: number;    // Type 'number' is not assignable to 'string'
    }

Legacy decorators receive (target: any, key: string) and lose the field type
entirely, so this was impossible in v1. Standard decorators receive
ClassFieldDecoratorContext<This, Value>, which carries it. Rules now checked:
scalar rules against scalar fields; { each: true } against arrays, in both
directions; @JsonType against the field's class; @JsonSerialize/@JsonDeserialize
against the field's type; @IsIn and @IsEnum against the field's value type.

17 tests invoke the real compiler to assert the wrong code stays rejected — a
guarantee nobody checks is one that quietly stops holding.

Positioning follows the capability: validated domain objects, not validated
data. The README now leads with the Zod comparison. Cereale does not infer your
type from a schema — you still write the field type and the rule — but it
guarantees the two cannot disagree, which is what class-validator never offered.

Removed
- metadata-storage.ts and its WeakMap singleton. Metadata lives on
  context.metadata now, which also removes the dual ESM/CJS double-singleton
  hazard. Inheritance merging becomes structural rather than reconstructed on
  every read, so the subclass-shadowing defect fixed by hand in 0.1.0 cannot
  reoccur by construction.
- registerDecorator, replaced by defineRule(Class, 'field', constraint).

Unchanged: the engine, options, naming strategies, access control, error
helpers, the sync API, and the performance work. 193 tests pass.

Toolchain note: standard decorators are transformed by tsc and esbuild, but not
yet by oxc. The library builds with tsc and consumers on esbuild/Vite are fine;
Vitest 4 uses oxc, so the test runner needs an esbuild transform plugin. This is
recorded in vitest.config.ts and the README, and is the reason 1.x should stay
available for oxc-based toolchains.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SAcqrz3FcadkYr3xG32CjK

src/decorators.test.ts

@@ -13,7 +13,7 @@ import {
   ArrayMaxSize, 
   IsNotIn, 
   Validate, 
-  registerDecorator,
+  defineRule,
   JsonType,
   JsonPolymorphic,
   JsonMapper,
@@ -244,21 +244,14 @@ describe('Additional Decorators', () => {
 
   describe('registerDecorator', () => {
     it('should register a custom decorator with functional validator', async () => {
-      function IsEven() {
-        return function (object: any, propertyName: string) {
-          registerDecorator({
-            name: 'isEven',
-            target: object.constructor,
-            propertyName: propertyName,
-            validator: (value: any) => typeof value === 'number' && value % 2 === 0,
-          });
-        };
-      }
-
       class Test {
-        @IsEven()
-        val: number;
+        val: number = 0;
       }
+      defineRule(Test, 'val', {
+        name: 'isEven',
+        validate: (value: any) => typeof value === 'number' && value % 2 === 0,
+        message: 'val must be even',
+      });
 
       const t = new Test();
       t.val = 2;
@@ -271,19 +264,15 @@ describe('Additional Decorators', () => {
       class MyValidator implements ValidatorConstraintInterface {
         validate(v: any) { return v === 'ok'; }
       }
-      function IsOk() {
-        return function (object: any, propertyName: string) {
-          registerDecorator({
-            name: 'isOk',
-            target: object.constructor,
-            propertyName: propertyName,
-            validator: MyValidator,
-          });
-        };
-      }
       class Test {
-        @IsOk() val: string;
+        val: string = '';
       }
+      const validator = new MyValidator();
+      defineRule(Test, 'val', {
+        name: 'isOk',
+        validate: (v: any) => validator.validate(v),
+        message: 'val must be ok',
+      });
       const t = new Test();
       t.val = 'ok';
       expect(await JsonMapper.validate(t)).toHaveLength(0);