itest: Add reusable integration test library crate

Extract the test infrastructure pattern shared across bcvk, ostree,
composefs-rs, and bootc into a standalone library crate.  This follows
the direction outlined in bootc-dev/infra repository-structure.md to
reduce code duplication for integration testing.

The crate provides:

- Test registration via linkme distributed slices and integration_test!
  / parameterized_integration_test! macros (no manual test lists)
- Privilege dispatch via privileged_test! and booted_test! macros that
  auto-dispatch to bcvk VMs when not running as root
- JUnit XML output via quick-junit (set JUNIT_OUTPUT env var)
- A harness runner (run_tests / run_tests_with_config) that ties
  together libtest-mimic, parameterized test expansion, and JUnit

The integration-tests crate is updated to use itest instead of its own
hand-rolled infrastructure.  Test function return types are migrated
from color_eyre::Result to anyhow::Result to align with the library
standard (the tests never used color_eyre-specific features).

Assisted-by: OpenCode (Claude Opus 4.6)
Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

Cargo.lock

@@ -17,8 +17,10 @@ name = "test-cleanup"
 path = "src/bin/cleanup.rs"
 
 [dependencies]
+itest = { path = "../itest" }
 bcvk = { path = "../kit" }
-color-eyre = { workspace = true }
+anyhow = "1"
+linkme = "0.3"
 dirs = "5.0"
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
@@ -29,13 +31,10 @@ serde = { version = "1.0.199", features = ["derive"] }
 serde_json = "1.0.116"
 zlink = "0.4"
 tokio = { version = "1", features = ["rt", "net", "macros"] }
-libtest-mimic = "0.7.3"
 tempfile = "3"
 uuid = { version = "1.18.1", features = ["v4"] }
 camino = "1.1.12"
 regex = "1"
-linkme = "0.3.30"
-paste = "1.0"
 rand = { workspace = true }
 scopeguard = "1"
 cap-std-ext = { workspace = true }