message: add from impls for u32/usize
diff: @@ -38,6 +38,19 @@ impl Id {
  }
  }
  +impl From<u32> for Id {
  + fn from(n: u32) -> Self {
  + Id::from_u32(n)
  + }
  +}
  +
  +impl From<usize> for Id {
  + fn from(n: usize) -> Self {
  + assert!(n < Id::MAX_USIZE);
  + Id::from_u32(n as u32)
  + }
  +}
  +
  impl From<Id> for u32 {
  fn from(n: Id) -> Self {
  n.as_u32()
  