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/tui/tests/suite/status_indicator.rs

@@ -0,0 +1,24 @@
+//! Regression test: ensure that `StatusIndicatorWidget` sanitises ANSI escape
+//! sequences so that no raw `\x1b` bytes are written into the backing
+//! buffer.  Rendering logic is tricky to unit‑test end‑to‑end, therefore we
+//! verify the *public* contract of `ansi_escape_line()` which the widget now
+//! relies on.
+
+use codex_ansi_escape::ansi_escape_line;
+
+#[test]
+fn ansi_escape_line_strips_escape_sequences() {
+    let text_in_ansi_red = "\x1b[31mRED\x1b[0m";
+
+    // The returned line must contain three printable glyphs and **no** raw
+    // escape bytes.
+    let line = ansi_escape_line(text_in_ansi_red);
+
+    let combined: String = line
+        .spans
+        .iter()
+        .map(|span| span.content.to_string())
+        .collect();
+
+    assert_eq!(combined, "RED");
+}