ci: align Bazel repo cache and Windows clippy target handling (#16740)

## Why

Bazel CI had two independent Windows issues:

- The workflow saved/restored `~/.cache/bazel-repo-cache`, but
`.bazelrc` configured `common:ci-windows
--repository_cache=D:/a/.cache/bazel-repo-cache`, so `actions/cache` and
Bazel could point at different directories.
- The Windows `Bazel clippy` job passed the full explicit target list
from `//codex-rs/...`, but some of those explicit targets are
intentionally incompatible with `//:local_windows`.
`run-argument-comment-lint-bazel.sh` already handles that with
`--skip_incompatible_explicit_targets`; the clippy workflow path did
not.

I also tried switching the workflow cache path to
`D:\a\.cache\bazel-repo-cache`, but the Windows clippy job repeatedly
failed with `Failed to restore: Cache service responded with 400`, so
the final change standardizes on `$HOME/.cache/bazel-repo-cache` and
makes cache restore non-fatal.

## What Changed

- Expose one repository-cache path from
`.github/actions/setup-bazel-ci/action.yml` and export that path as
`BAZEL_REPOSITORY_CACHE` so `run-bazel-ci.sh` passes it to Bazel after
`--config=ci-*`.
- Move `actions/cache/restore` out of the composite action into
`.github/workflows/bazel.yml`, and make restore failures non-fatal
there.
- Save exactly the exported cache path in `.github/workflows/bazel.yml`.
- Remove `common:ci-windows
--repository_cache=D:/a/.cache/bazel-repo-cache` from `.bazelrc` so the
Windows CI config no longer disagrees with the workflow cache path.
- Pass `--skip_incompatible_explicit_targets` in the Windows `Bazel
clippy` job so incompatible explicit targets do not fail analysis while
the lint aspect still traverses compatible Rust dependencies.

## Verification

- Parsed `.github/actions/setup-bazel-ci/action.yml` and
`.github/workflows/bazel.yml` with Ruby's YAML loader.
- Resubmitted PR `#16740`; CI is rerunning on the amended commit.

.github/workflows/README.md

@@ -5,15 +5,15 @@ The workflows in this directory are split so that pull requests get fast, review
 ## Pull Requests
 
 - `bazel.yml` is the main pre-merge verification path for Rust code.
-  It runs Bazel `test` and Bazel `clippy` on the supported Bazel targets.
+  It runs Bazel `test` and Bazel `clippy` on the supported Bazel targets,
+  including the generated Rust test binaries needed to lint inline `#[cfg(test)]`
+  code.
 - `rust-ci.yml` keeps the Cargo-native PR checks intentionally small:
   - `cargo fmt --check`
   - `cargo shear`
   - `argument-comment-lint` on Linux, macOS, and Windows
   - `tools/argument-comment-lint` package tests when the lint or its workflow wiring changes
 
-The PR workflow still keeps the Linux lint lane on the default-targets-only invocation for now, but the released linter runs on Linux, macOS, and Windows before merge.
-
 ## Post-Merge On `main`
 
 - `bazel.yml` also runs on pushes to `main`.