ci: fuzzers in the Github Actions CI. (#29)

* Add fuzzing CI.

* fuzz dependency change: diffutils -> diffutilslib

* fix fuzz build.

.github/workflows/fuzzing.yml

@@ -0,0 +1,72 @@
+name: Fuzzing
+
+# spell-checker:ignore fuzzer
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  fuzz-build:
+    name: Build the fuzzers
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - name: Install `cargo-fuzz`
+        run: cargo install cargo-fuzz
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: "cargo-fuzz-cache-key"
+          cache-directories: "fuzz/target"
+      - name: Run `cargo-fuzz build`
+        run: cargo +nightly fuzz build
+
+  fuzz-run:
+    needs: fuzz-build
+    name: Run the fuzzers
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    env:
+      RUN_FOR: 60
+    strategy:
+      matrix:
+        test-target:
+          - { name: fuzz_ed, should_pass: true }
+          - { name: fuzz_normal, should_pass: true }
+          - { name: fuzz_patch, should_pass: true }
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - name: Install `cargo-fuzz`
+        run: cargo install cargo-fuzz
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: "cargo-fuzz-cache-key"
+          cache-directories: "fuzz/target"
+      - name: Restore Cached Corpus
+        uses: actions/cache/restore@v4
+        with:
+          key: corpus-cache-${{ matrix.test-target.name }}
+          path: |
+            fuzz/corpus/${{ matrix.test-target.name }}
+      - name: Run ${{ matrix.test-target.name }} for XX seconds
+        shell: bash
+        continue-on-error: ${{ !matrix.test-target.name.should_pass }}
+        run: |
+          cargo +nightly fuzz run ${{ matrix.test-target.name }} -- -max_total_time=${{ env.RUN_FOR }} -detect_leaks=0
+      - name: Save Corpus Cache
+        uses: actions/cache/save@v4
+        with:
+          key: corpus-cache-${{ matrix.test-target.name }}
+          path: |
+            fuzz/corpus/${{ matrix.test-target.name }}