This also changes the DSN to a heap allocated, refcounted type since
the http worker thread needs to hold onto its own reference.

this now decouples preparing an event, which also removes the need for a special breakpad transport and mutating the global transport. Also the crashed session is now attached to the crashed envelope, and has a correct errors count

options are now refcounted internally instead of taking locks for long times. the user consent is now done as an atomic operation.