bazel: lint rust_test targets in clippy workflow (#16450)

## Why

`cargo clippy --tests` was catching warnings in inline `#[cfg(test)]`
code that the Bazel PR Clippy lane missed. The existing Bazel invocation
linted `//codex-rs/...`, but that did not apply Clippy to the generated
manual `rust_test` binaries, so warnings in targets such as
`//codex-rs/state:state-unit-tests-bin` only surfaced as plain compile
warnings instead of failing the lint job.

## What Changed

- added `scripts/list-bazel-clippy-targets.sh` to expand the Bazel
Clippy target set with the generated manual `rust_test` rules while
still excluding `//codex-rs/v8-poc:all`
- updated `.github/workflows/bazel.yml` to use that expanded target list
in the Bazel Clippy PR job
- updated `just bazel-clippy` to use the same target expansion locally
- updated `.github/workflows/README.md` to document that the Bazel PR
lint lane now covers inline `#[cfg(test)]` code

## Verification

- `./scripts/list-bazel-clippy-targets.sh` includes
`//codex-rs/state:state-unit-tests-bin`
- `bazel build --config=clippy -- //codex-rs/state:state-unit-tests-bin`
now fails with the same unused import in `state/src/runtime/logs.rs`
that `cargo clippy --tests` reports