feat: Run cargo shear during CI (#3338)

Run cargo shear as part of the CI to ensure no unused dependencies

codex-rs/mcp-server/Cargo.toml

@@ -26,7 +26,6 @@ schemars = "0.8.22"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 shlex = "1.3.0"
-strum_macros = "0.27.2"
 tokio = { version = "1", features = [
     "io-std",
     "macros",
@@ -44,5 +43,4 @@ assert_cmd = "2"
 mcp_test_support = { path = "tests/common" }
 pretty_assertions = "1.4.1"
 tempfile = "3"
-tokio-test = "0.4"
 wiremock = "0.6"