ci: stop running rust CI with --all-features (#16473)

## Why

Now that workspace crate features have been removed and
`.github/scripts/verify_cargo_workspace_manifests.py` hard-bans new
ones, Rust CI should stop building and testing with `--all-features`.

Keeping `--all-features` in CI no longer buys us meaningful coverage for
`codex-rs`, but it still makes the workflow look like we rely on Cargo
feature permutations that we are explicitly trying to eliminate. It also
leaves stale examples in the repo that suggest `--all-features` is a
normal or recommended way to run the workspace.

## What changed

- removed `--all-features` from the Rust CI `cargo chef cook`, `cargo
clippy`, and `cargo nextest` invocations in
`.github/workflows/rust-ci-full.yml`
- updated the `just test` guidance in `justfile` to reflect that
workspace crate features are banned and there should be no need to add
`--all-features`
- updated the multiline command example and snapshot in
`codex-rs/tui/src/history_cell.rs` to stop rendering `cargo test
--all-features --quiet`
- tightened the verifier docstring in
`.github/scripts/verify_cargo_workspace_manifests.py` so it no longer
talks about temporary remaining exceptions

## How tested

- `python3 .github/scripts/verify_cargo_workspace_manifests.py`
- `cargo test -p codex-tui`

codex-rs/tui/src/history_cell.rs

@@ -4057,7 +4057,7 @@ mod tests {
     #[test]
     fn multiline_command_wraps_with_extra_indent_on_subsequent_lines() {
         // Create a completed exec cell with a multiline command
-        let cmd = "set -o pipefail\ncargo test --all-features --quiet".to_string();
+        let cmd = "set -o pipefail\ncargo test -p codex-tui --quiet".to_string();
         let call_id = "c1".to_string();
         let mut cell = ExecCell::new(
             ExecCall {
@@ -4075,7 +4075,7 @@ mod tests {
         // Mark call complete so it renders as "Ran"
         cell.complete_call(&call_id, CommandOutput::default(), Duration::from_millis(1));
 
-        // Small width to force wrapping on both lines
+        // Small width to keep the wrapped continuation-indent path covered.
         let width: u16 = 28;
         let lines = cell.display_lines(width);
         let rendered = render_lines(&lines).join("\n");

codex-rs/tui/src/snapshots/codex_tui__history_cell__tests__multiline_command_wraps_with_extra_indent_on_subsequent_lines.snap

@@ -3,6 +3,6 @@ source: tui/src/history_cell.rs
 expression: rendered
 ---
 • Ran set -o pipefail
-  │ cargo test
-  │ --all-features --quiet
+  │ cargo test -p codex-tui
+  │ --quiet
   └ (no output)