ci: add GitHub Actions for CI, release, and hex publishing

Author: fahchen

.github/workflows/elixir.yml

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+name: Elixir CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_name }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    env:
+      FORCE_COLOR: 1
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - elixir: 1.18.0
+            otp: 27.2
+          - elixir: 1.17.3
+            otp: 27.2
+            lint: lint
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install Elixir and Erlang
+        uses: erlef/setup-beam@v1
+        with:
+          elixir-version: ${{ matrix.elixir }}
+          otp-version: ${{ matrix.otp }}
+      - name: Restore deps, _build and plts cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            deps
+            _build
+          key: ${{ runner.os }}-${{ matrix.elixir }}-${{ matrix.otp }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ matrix.elixir }}-${{ matrix.otp }}-
+
+      - name: Install dependencies
+        run: mix deps.get
+      - name: Compile deps
+        run: mix deps.compile
+
+      - name: Check format
+        run: mix format --check-formatted
+        if: ${{ matrix.lint }}
+
+      - name: Check unused dependencies
+        run: mix deps.unlock --check-unused
+        if: ${{ matrix.lint }}
+
+      - name: Compile lint
+        run: mix compile --warnings-as-errors
+        if: ${{ matrix.lint }}
+
+      - name: Dialyzer
+        run: mix dialyzer --format github
+        if: ${{ matrix.lint }}
+
+      - name: Run tests
+        run: mix test --cover
+        if: ${{ matrix.lint }}
+
+      - name: Run tests
+        run: mix test
+        if: ${{ !matrix.lint }}

.github/workflows/publish.yml

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+name: Publish
+
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: erlef/setup-beam@v1
+        with:
+          elixir-version: 1.17.3
+          otp-version: 27.2
+
+      - run: mix deps.get
+      - run: mix hex.build
+      - run: mix hex.publish --yes --replace
+        env:
+          HEX_API_KEY: ${{ secrets.HEX_API_KEY }}

.github/workflows/release.yml

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+name: Release
+
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: googleapis/release-please-action@v4
+        with:
+          release-type: elixir
+          skip-github-release: true