feat(build): add extism-maturin wheel builds (#480)

Build the python native library along with libextism since they change
at roughly the same rate; we can pull the resulting wheels into
python-sdk as needed.

Reduce the release job into a single matrix of `OS x RUST TARGET` – this
unifies the macos, windows, and linux builds into a single job.

---

**BREAKING CHANGE**: This changes the trigger for the release workflow.
Instead of being triggered by the creation of a release, it is triggered
by pushing new git tags. It will catch `v*` – `v0.5.0`, `v200.0.1-dev`
for example. The workflow creates a draft release.

Cargo.toml

@@ -1,5 +1,6 @@
 [workspace]
 members = [
+  "extism-maturin",
   "manifest",
   "runtime",
   "libextism",