Add file.write

rt/include/python/builtins.hpp

@@ -145,6 +145,14 @@ struct {
           buf.resize(nbytes);
           co_return std::move(buf);
         })
+    METHOD(
+        typon::Task<int>, write, (const std::string &buf), const {
+          int nbytes = co_await typon::io::write(self->fd, buf);
+          if (nbytes < 0) {
+            system_error(-nbytes, "write()");
+          }
+          co_return nbytes;
+        })
     METHOD(
         typon::Task<void>, close, (),
         const { co_await typon::io::close(self->fd); })