Refactor integration test core into a new 'obo-tests' crate

Most of this logic is rather intricate and shareable between multiple
implementations, so it makes sense for them to be in a separate crate.
This necessitates quite a bit of refactoring of the test structure so
that the shared test code can actually run commands and inspect the
logs + artifacts. Since there are various somewhat strange requirements
around command execution (i.e. needing to use timeouts but still get the
result), that API was redone around a builder trait, which also makes it
easy for implementation-specific tests to have their own methods on it.

Author: refi64

Cargo.lock

@@ -2,6 +2,7 @@
 resolver = "3"
 members = [
   "obo-core",
+  "obo-tests",
   "obo-test-support",
   "obs-gitlab-runner"
 ]

Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "obo-tests"
+description = "OBS Build Orchestrator — shared tests for different frontends"
+version = "0.1.0"
+edition = "2024"
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+async-trait.workspace = true
+camino.workspace = true
+claims.workspace = true
+obo-core = { path = "../obo-core" }
+obo-test-support = { path = "../obo-test-support" }
+open-build-service-api.workspace = true
+open-build-service-mock.workspace = true
+serde_yaml.workspace = true
+tokio.workspace = true