Add BYD vehicle telemetry exporter

Go port of the read path of pybyd 0.0.75 (the client behind
jkaberg/hass-byd-vehicle): the bangcle white-box AES envelope, the
signing/checkcode layer, login, vehicle list, and realtime readings.

Scraping runs on a cron schedule rather than per Prometheus request
because each reading wakes the car's T-Box and drains the traction
battery; /metrics serves the last result.

Every numeric field of the realtime payload becomes a gauge, so the
exporter does not need a hand-maintained field list that goes stale
when BYD changes the payload.

Tests pin the wire format against pybyd byte-for-byte and drive the
client end to end against a fake cloud that speaks the real protocol.

Co-Authored-By: Claude Opus 5 <[email protected]>

.gitea/workflows/release.yml

@@ -0,0 +1,32 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: read
+  actions: read
+  packages: write
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/[email protected]
+      - uses: actions/setup-go@v5
+        with:
+          go-version: '1.22'
+      - run: go vet ./... && go test -race ./...
+
+  build:
+    needs: test
+    uses: infras/workflow-templates/.gitea/workflows/docker-template.yml@736cd715b4b9c80f20ec51ef8445cb630c8299f5
+    with:
+      image_name: byd-exporter
+      image_owner: thistine
+      image_tag: ${{ gitea.ref_name }}
+    secrets:
+      REGISTRY_USER: ${{ secrets.REGISTRY_USER }}
+      REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}

.gitea/workflows/test.yml

@@ -0,0 +1,19 @@
+name: Test
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/[email protected]
+      - uses: actions/setup-go@v5
+        with:
+          go-version: '1.22'
+      - name: gofmt
+        run: test -z "$(gofmt -l .)" || { gofmt -l .; exit 1; }
+      - run: go vet ./...
+      - run: go test -race -cover ./...