bump version to v0.3.1 (#46)

Unlike the `v0.3.1` tag I just pushed, this leaves the Go wrapper pointing to
the "canary" release rather than the `v0.3.1` release, since this PR targets the
`main` branch.

Author: dicej

Cargo.lock

@@ -19,7 +19,7 @@ reqwest = { version = "0.13.1", features = ["blocking"] }
 tar = "0.4"
 
 [workspace.package]
-version = "0.3.0"
+version = "0.3.1"
 edition = "2024"
 
 [workspace.lints.clippy]