fix: changed subscribe transformer to have same client/server code

[agliga]

Scope

There is a cache issue where transformers would run compile on server and then not compile on browser again. So fixed subscribe to do a check if it's running in the browser in order to get the to attribute.

Checklist:

• [X] I have updated/added documentation affected by my changes.
• [X] I have added tests to cover my changes.