[codex] Revert shared BuildBuddy Bazel wrapper (#25909)

## Why

PR #25905 intentionally adds a failing `codex-core` unit test, but its
[Bazel test on Windows
check](https://github.com/openai/codex/actions/runs/26837526950/job/79135369259)
passed. That shows the Bazel configuration introduced by #25156 is not
behaving as expected, so revert it while the configuration can be
investigated separately.

## What changed

Revert #25156 in full, restoring the previous Bazel remote
configuration, CI scripts, workflows, `rusty_v8` handling, and
documentation. This removes the shared BuildBuddy wrapper and its tests.

## Validation

Not run locally; this exact revert was prioritized for a fast rollback.

.github/workflows/bazel.yml

@@ -15,7 +15,6 @@ concurrency:
   # See https://docs.github.com/en/actions/using-jobs/using-concurrency and https://docs.github.com/en/actions/learn-github-actions/contexts for more info.
   group: concurrency-group::${{ github.workflow }}::${{ github.event.pull_request.number > 0 && format('pr-{0}', github.event.pull_request.number) || github.ref_name }}${{ github.ref_name == 'main' && format('::{0}', github.run_id) || ''}}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
-
 jobs:
   test:
     # PRs use the sharded Windows cross-compiled test jobs below. Post-merge
@@ -56,17 +55,12 @@ jobs:
           ref: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.sha }}
           persist-credentials: false
 
-      - uses: taiki-e/install-action@44c6d64aa62cd779e873306675c7a58e86d6d532 # v2.62.49
-        if: matrix.os == 'ubuntu-24.04' && matrix.target == 'x86_64-unknown-linux-gnu'
-        with:
-          tool: just
-
       - name: Check rusty_v8 MODULE.bazel checksums
         if: matrix.os == 'ubuntu-24.04' && matrix.target == 'x86_64-unknown-linux-gnu'
         shell: bash
         run: |
           python3 .github/scripts/rusty_v8_bazel.py check-module-bazel
-          just test-github-scripts
+          python3 -m unittest discover -s .github/scripts -p test_rusty_v8_bazel.py
 
       - name: Prepare Bazel CI
         id: prepare_bazel

.github/workflows/rusty-v8-release.yml

@@ -191,10 +191,11 @@ jobs:
             bazel_args+=(--config=v8-release-compat)
           fi
 
-          ./.github/scripts/run_bazel_with_buildbuddy.py \
+          bazel \
             --noexperimental_remote_repo_contents_cache \
             "${bazel_args[@]}" \
-            "--config=${{ matrix.bazel_config }}"
+            "--config=${{ matrix.bazel_config }}" \
+            "--remote_header=x-buildbuddy-api-key=${BUILDBUDDY_API_KEY}"
 
       - name: Stage release pair
         env:

.github/workflows/v8-canary.yml

@@ -5,7 +5,6 @@ on:
     paths:
       - ".bazelrc"
       - ".github/actions/setup-bazel-ci/**"
-      - ".github/scripts/run_bazel_with_buildbuddy.py"
       - ".github/scripts/rusty_v8_bazel.py"
       - ".github/scripts/rusty_v8_module_bazel.py"
       - ".github/workflows/rusty-v8-release.yml"
@@ -24,7 +23,6 @@ on:
     paths:
       - ".bazelrc"
       - ".github/actions/setup-bazel-ci/**"
-      - ".github/scripts/run_bazel_with_buildbuddy.py"
       - ".github/scripts/rusty_v8_bazel.py"
       - ".github/scripts/rusty_v8_module_bazel.py"
       - ".github/workflows/rusty-v8-release.yml"
@@ -205,10 +203,11 @@ jobs:
             bazel_args+=(--config=v8-release-compat)
           fi
 
-          ./.github/scripts/run_bazel_with_buildbuddy.py \
+          bazel \
             --noexperimental_remote_repo_contents_cache \
             "${bazel_args[@]}" \
-            "--config=${{ matrix.bazel_config }}"
+            "--config=${{ matrix.bazel_config }}" \
+            "--remote_header=x-buildbuddy-api-key=${BUILDBUDDY_API_KEY}"
 
       - name: Stage release pair
         env: