Add bazel CI workflow

.bazelignore

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+test/bazel

.github/workflows/bazel.yml

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+name: Bazel CI
+on: [push, pull_request, workflow_dispatch]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    uses: bazel-contrib/.github/.github/workflows/bazel.yaml@v7
+    with:
+      folders: |
+        [
+          ".",
+          "test/bazel",
+        ]
+      exclude: |
+        [
+          {"folder": ".", "bzlmodEnabled": false},
+          {"folder": "test/bazel", "bzlmodEnabled": false},
+        ]

.github/workflows/ci.bazelrc

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+# This file contains Bazel settings to apply on CI only.
+# It is referenced with a --bazelrc option in the call to bazel in ci.yaml
+
+# Debug where options came from
+build --announce_rc
+
+# This directory is configured in GitHub actions to be persisted between runs.
+# We do not enable the repository cache to cache downloaded external artifacts
+# as these are generally faster to download again than to fetch them from the
+# GitHub actions cache.
+build --disk_cache=~/.cache/bazel
+
+# Don't rely on test logs being easily accessible from the test runner,
+# though it makes the log noisier.
+test --test_output=errors
+
+# Allows tests to run bazelisk-in-bazel, since this is the cache folder used
+test --test_env=XDG_CACHE_HOME

test/bazel/BUILD.bazel

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+load("@xacro//:build_defs.bzl", "xacro")

test/bazel/MODULE.bazel

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+bazel_dep(name = "xacro")
+local_path_override(
+    module_name = "xacro",
+    path = "../..",
+)