Store sub_type as a [*c]const u8

Makes the @sizeof(ExternalEntry) 16, instead of 24 and works just as well
with the string literal we expect it to be set to.

Author: karlseguin

src/engines/v8/v8.zig

@@ -717,7 +717,7 @@ pub const ExternalEntry = struct {
     // the proper subtype (and description) fields in the returned JSON.
     // V8 will give us a Value and ask us for the subtype. Hence, we store it
     // here.
-    sub_type: ?[:0]const u8,
+    sub_type: ?[*c]const u8,
 };
 
 // See above for documentation for the ExternalEntry's sub_type field.

src/reflect.zig

@@ -785,7 +785,7 @@ pub const Struct = struct {
 
     // nested types
     nested: []const StructNested,
-    sub_type: ?[:0]const u8,
+    sub_type: ?[*c]const u8,
 
     pub fn Self(comptime self: Struct) type {
         comptime {
@@ -1247,7 +1247,7 @@ pub const Struct = struct {
             mem_guarantied = @typeInfo(T).@"struct".layout != .auto;
         }
 
-        var sub_type: ?[:0]const u8 = null;
+        var sub_type: ?[*c]const u8 = null;
         if (@hasDecl(T, "sub_type")) {
             sub_type = @field(T, "sub_type");
         }