Add BCR workflow for Bazel Central Registry publishing

Signed-off-by: Matthieu MOREL <matthieu.morel35@gmail.com>

Author: mmorel-35

.bcr/metadata.template.json

@@ -0,0 +1,16 @@
+{
+    "homepage": "https://github.com/fastfloat/fast_float",
+    "maintainers": [
+        {
+            "email": "byvoid@byvoid.com",
+            "github": "BYVoid",
+            "name": "Carbo Kuo",
+            "github_user_id": 245270
+        }
+    ],
+    "repository": [
+        "github:fastfloat/fast_float"
+    ],
+    "versions": [],
+    "yanked_versions": {}
+}

.bcr/presubmit.yml

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+matrix:
+  platform:
+  - debian10
+  - ubuntu2004
+  - ubuntu2204
+  - macos
+  - macos_arm64
+  - windows
+  bazel:
+  - 9.*
+  - 8.x
+  - 7.x
+  - 6.x
+tasks:
+  verify_targets:
+    name: Verify build targets
+    platform: ${{ platform }}
+    bazel: ${{ bazel }}
+    build_targets:
+    - '@fast_float'

.bcr/source.template.json

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+{
+    "integrity": "",
+    "strip_prefix": "{REPO}-{VERSION}",
+    "url": "https://github.com/{OWNER}/{REPO}/archive/refs/tags/v{VERSION}.tar.gz"
+}

.github/workflows/publish-to-bcr.yml

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+name: Publish to BCR
+
+on:
+  release:
+    types: [published]
+
+  # Allow manual triggering from GH UI
+  workflow_dispatch:
+    inputs:
+      tag_name:
+        description: 'Tag name to publish (e.g., v1.2.3)'
+        required: true
+        type: string
+
+permissions:
+  id-token: write
+  attestations: write
+  contents: write
+
+jobs:
+  publish:
+    uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@v1.0.0
+    with:
+      tag_name: ${{ github.event.release.tag_name || inputs.tag_name }}
+    secrets:
+      publish_token: ${{ secrets.BCR_PUBLISH_TOKEN }}