Remove bool return from runWeavelet

[dnephin]

While browsing the code I noticed that the bool return from Envelope.runWeavelet was always false. Removing the return value simplifies the caller slightly. I'm opening this PR to see if you are interested in this small simplification. Thanks for considering it!

I often try to avoid (bool, error) returns, and opt to use a sentinel error value when possible. That may be an option in the future if runWeavelet needs to indicate a speicific error case.

[mwhittaker]

GitHub says this branch is out-of-date with the base branch. Mind rebasing and squashing on top of main?

[dnephin]

Rebase and squash done!