[orchestra] fix: require the initialization with `F: FnOnce` to be `Send` (#6051)

* add regression test for missing Send requirement

* fix: require the initialization with `F: FnOnce` to be `Send` as well

If creating intermediate variables of the builder type within
a future, rustc will complain about the future not being send,
while the thing itself isn't even using the closure based field
initialization. Adding an additional bound, resolves this and
pushes the error message "closer" to the user, and out of the
generated code.

* import fixins