HMAC Push notification updates

[nplasterer]

Adding the new HMAC code to the example and push classes to help make this easier.

See typescript docs here: https://github.com/xmtp/example-notification-server-go/blob/main/docs/notifications-client-guide.md

[zombieobject]

@nplasterer I am currently looking into the build for test failures. From what I can see in the logs, the pipeline never gets to the test stage. I will update once I figure out the source. Going to switch to local builds to isolate it for now.

[zombieobject]

@nplasterer Something is off with the protobuf code generation in service.connect.swift that is causing build errors. Additionally, build for test fails as well, but I can't resolve those until the protobuf issue is corrected. See review comments inline for further details and LMK how I can help. 👨🏼‍🚒

[zombieobject]

The changes by @kele-leanes to update the connect-swift package addressed the protobuf questions. Additionally, some rearrangement of the if/def fencing in XMTPPush.swift fixed the typealias visibility when building for test in CI.

[nplasterer]

I was hoping to have more time to validate this this week but going to merge in favor unblocking integrators and will follow up with any tweaks once I've fully validated on Android.