fix: module imports optional types

[DemonHa]

Currently Module.Import types are not working correctly when we wrap the Record type with an optional field.

See example:

const UserSchema = Type.Object({
  id: Type.String({ format: "uuid" }),
  email: Type.String({ format: "email" }),
  account: Type.Optional(Type.Ref("Account")),
});

const AccountSchema = Type.Object({
  id: Type.String({ format: "uuid" }),
  name: Type.String(),
  users: Type.Array(Type.Ref("User")),
  events: Type.Optional(
    Type.Record(
      Type.String(), // event name (e.g. "user.created")
      Type.Object({
        message: Type.Union([
          Type.Literal("welcome"),
          Type.Literal("reminder"),
        ]),
      })
    )
  ),
});

const Module = Type.Module({
  User: UserSchema,
  Account: AccountSchema,
});

const Account = Module.Import("Account");

// Wrong type:
// events?: {} | undefined;
type AccountType = Static<typeof Account>;

This PR fixes the types to return the correct type for this specific case