test: faster test execution in codex-core (#2633)

this dramatically improves time to run `cargo test -p codex-core` (~25x
speedup).

before:
```
cargo test -p codex-core  35.96s user 68.63s system 19% cpu 8:49.80 total
```

after:
```
cargo test -p codex-core  5.51s user 8.16s system 63% cpu 21.407 total
```

both tests measured "hot", i.e. on a 2nd run with no filesystem changes,
to exclude compile times.

approach inspired by [Delete Cargo Integration
Tests](https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html),
we move all test cases in tests/ into a single suite in order to have a
single binary, as there is significant overhead for each test binary
executed, and because test execution is only parallelized with a single
binary.

codex-rs/execpolicy/tests/suite/pwd.rs

@@ -0,0 +1,86 @@
+extern crate codex_execpolicy;
+
+use std::vec;
+
+use codex_execpolicy::Error;
+use codex_execpolicy::ExecCall;
+use codex_execpolicy::MatchedExec;
+use codex_execpolicy::MatchedFlag;
+use codex_execpolicy::Policy;
+use codex_execpolicy::PositionalArg;
+use codex_execpolicy::ValidExec;
+use codex_execpolicy::get_default_policy;
+
+#[expect(clippy::expect_used)]
+fn setup() -> Policy {
+    get_default_policy().expect("failed to load default policy")
+}
+
+#[test]
+fn test_pwd_no_args() {
+    let policy = setup();
+    let pwd = ExecCall::new("pwd", &[]);
+    assert_eq!(
+        Ok(MatchedExec::Match {
+            exec: ValidExec {
+                program: "pwd".into(),
+                ..Default::default()
+            }
+        }),
+        policy.check(&pwd)
+    );
+}
+
+#[test]
+fn test_pwd_capital_l() {
+    let policy = setup();
+    let pwd = ExecCall::new("pwd", &["-L"]);
+    assert_eq!(
+        Ok(MatchedExec::Match {
+            exec: ValidExec {
+                program: "pwd".into(),
+                flags: vec![MatchedFlag::new("-L")],
+                ..Default::default()
+            }
+        }),
+        policy.check(&pwd)
+    );
+}
+
+#[test]
+fn test_pwd_capital_p() {
+    let policy = setup();
+    let pwd = ExecCall::new("pwd", &["-P"]);
+    assert_eq!(
+        Ok(MatchedExec::Match {
+            exec: ValidExec {
+                program: "pwd".into(),
+                flags: vec![MatchedFlag::new("-P")],
+                ..Default::default()
+            }
+        }),
+        policy.check(&pwd)
+    );
+}
+
+#[test]
+fn test_pwd_extra_args() {
+    let policy = setup();
+    let pwd = ExecCall::new("pwd", &["foo", "bar"]);
+    assert_eq!(
+        Err(Error::UnexpectedArguments {
+            program: "pwd".to_string(),
+            args: vec![
+                PositionalArg {
+                    index: 0,
+                    value: "foo".to_string()
+                },
+                PositionalArg {
+                    index: 1,
+                    value: "bar".to_string()
+                },
+            ],
+        }),
+        policy.check(&pwd)
+    );
+}