fix(core): ensure strict type-checking of enum queries

The `FilterQuery` type mistakenly allowed any string values in place of an enum.

This fix now enforces correct values, which also for TS `enum` means using the string
value is no longer possible:

```ts
// this will fail if `type` is a TS enum (but will work with a string union)
await em.find(User, { type: 'admin' });
```

packages/core/src/typings.ts

@@ -61,7 +61,7 @@ export type IPrimaryKey<T extends IPrimaryKeyValue = IPrimaryKeyValue> = T;
 export type Scalar = boolean | number | string | bigint | symbol | Date | RegExp | Buffer | { toHexString(): string };
 
 export type ExpandScalar<T> = null | (T extends string
-  ? string | RegExp
+  ? T | RegExp
   : T extends Date
     ? Date | string
     : T);

tests/types.test.ts

@@ -324,6 +324,44 @@ describe('check typings', () => {
     ok01 = { rels: ['abc'] };
   });
 
+  test('FilterQuery with ', async () => {
+    enum ABC {
+      A,
+      B,
+      C,
+    }
+
+    enum DEF {
+      D = 'd',
+      E = 'e',
+      F = 'f',
+    }
+
+    interface Publisher {
+      id: string;
+      enum1: 'a' | 'b' | 'c';
+      enum2: ABC;
+      enum3: DEF;
+    }
+
+    let query: FilterQuery<Publisher>;
+    query = { enum1: 'a' };
+    query = { enum1: 'b' };
+    // @ts-expect-error
+    query = { enum1: 'd' };
+    query = { enum2: ABC.A };
+    // @ts-expect-error
+    query = { enum2: 'a' };
+    query = { enum2: ABC.A };
+    // @ts-expect-error
+    query = { enum2: DEF.D };
+    // @ts-expect-error
+    query = { enum3: 'd' };
+    // @ts-expect-error
+    query = { enum3: ABC.A };
+    query = { enum3: DEF.D };
+  });
+
   test('AutoPath with optional nullable properties', async () => {
     interface MessageRecipient {
       id: string;