update newtype access syntax

[Guest0x0]

No description provided.

[peter-jerry-ye-code-review]

From the provided git diff output, I observe the following issues related to MoonBit language usage:

1. Incorrect Field Access for Newtypes:

   • The original code uses id.0 to access the internal representation of a newtype UserId. However, the MoonBit documentation suggests using id._ for this purpose.
   • Affected lines:

     - let uid: Int = id.0
     + let uid: Int = id._

2. Error Handling with Newtypes:

   • The function f attempts to raise an error using self.0 to access the internal representation of a newtype T. This should be corrected to use self._.
   • Affected lines:

     - fn f(self: T) -> Unit!E { raise E(self.0) }
     + fn f(self: T) -> Unit!E { raise E(self._) }

3. String Concatenation with Newtypes:

   • In the speak function for the Duck type, the code uses self.0 to access the internal string representation. This should be corrected to use self._.
   • Affected lines:

     - println(self.0 + ": quack!")
     + println(self._ + ": quack!")

These changes ensure that the code adheres to the MoonBit language conventions for accessing the internal representation of newtypes, which is crucial for maintaining consistency and avoiding potential runtime errors.