Fix all deprecation warnings & restructure targets making TelemetryDeck main one

[Jeehut]

Fixes #176.

Previously, when I added the new TelemetryDeck target to the package, I conservatively kept all the main code inside the old TelemetryClient target and imported TelemetryClient into TelemetryDeck. I was also hesitant to rename the package at the top level from TelemetryClient to TelemetryDeck, just to be sure not too many changes happen at once leading to too much frustration.

The outcome was that we were still using the old methods and calling them from the old ones, leading to deprecation warnings inside the package itself. In this PR, I went the next steps and moved the main logic into the new methods, so that the old methods are now calling into the new ones, making away with all the deprecation warnings. I also moved all the files from the TelemetryClient target into the TelemetryDeck target and reversed which target was importing which.

Additionally, I also renamed the package from TelemetryClient to TelemetryDeck. This should not have any consequences for Xcode users as Xcode should automatically pick up any package name changes. I've tested this in the feature/fix-warnings branch in the PirateMetrics repo. It should also not affect any Swift packages that depend on our SDK, such as server apps, because they specify the repo name SwiftSDK which hasn't changed, like so:

.product(name: "TelemetryDeck", package: "SwiftSDK")

So I believe that everything should continue to work and the hiccups for users should be minimal. But it's still worth asking for user feedback when this change is released in a future version, maybe even before on the main branch.

Note: CI was failing for visionOS due to this GitHub Actions issue, so I had to update the macOS version to 15 and then also Xcode version to 16 since Xcode 15 isn't officially supported on macOS 15.

[winsmith]

Love the cleanup work here! I just tested this on my machine both by including it in a project and building it myself. So satisfying to see the warnings gone!

[Jeehut]

@winsmith Quickly rebased to fix the merge conflicts due to the version bump in release 2.4.0.