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`

justfile

@@ -46,8 +46,8 @@ install:
 # --no-fail-fast is important to ensure all tests are run.
 #
 # Run `cargo install cargo-nextest` if you don't have it installed.
-# Prefer this for routine local runs; use explicit `cargo test --all-features`
-# only when you specifically need full feature coverage.
+# Prefer this for routine local runs. Workspace crate features are banned, so
+# there should be no need to add `--all-features`.
 test:
     cargo nextest run --no-fail-fast