fixing upcasting signed to unsigned

lang/README.md

@@ -842,6 +842,11 @@ integer_range := fn(min: uint, max: uint): uint {
 }
 ```
 
+#### signed_to_unsigned_upcast
+```hb
+main := fn(): uint return @as(i32, 1)
+```
+
 #### writing_into_string
 ```hb
 outl := fn(): void {

lang/src/lib.rs

@@ -434,6 +434,7 @@ mod ty {
                 _ if oa.is_pointer() && ob.is_pointer() => return None,
                 _ if a.is_signed() && b.is_signed() || a.is_unsigned() && b.is_unsigned() => ob,
                 _ if a.is_unsigned() && b.is_signed() && a.repr() - U8 < b.repr() - I8 => ob,
+                _ if a.is_unsigned() && b.is_signed() && a.repr() - U8 > b.repr() - I8 => oa,
                 _ if oa.is_integer() && ob.is_pointer() && kind == TyCheck::BinOp => ob,
                 _ => return None,
             })

lang/src/son.rs

@@ -4435,6 +4435,7 @@ mod tests {
         small_struct_assignment;
         intcast_store;
         string_flip;
+        signed_to_unsigned_upcast;
         wide_ret;
         comptime_min_reg_leak;
         different_types;