fix(types): preserve type narrowing in getSchemaValidator

[kimzuni]

When I used getSchemaValidator, I expected .Check() to properly narrow types as a type guard.

However, I found that because the return type uses ElysiaTypeCheck<TSchema> instead of ElysiaTypeCheck<T>, the type narrowing does not work correctly—even though T extends TSchema.

Example:

import { t, getSchemaValidator } from "elysia";

const schema = t.Object({
	key: t.String(),
});

const myData: Record<string, string> = {};

const validator = getSchemaValidator(schema);
const isValid = validator.Check(myData);

if (isValid) {
	myData; // is still inferred as Record<string, string>
}

After applying this fix, when isValid is true, myData is correctly narrowed to { key: string } inside the if block.

if (isValid) {
	myData; // is { key: string }
}