Use sqlean if available in environment (#560)

Closes #559
Closes #235

Refs https://github.com/simonw/llm/issues/60

- Uses `sqlean` in place of `sqlite3` if `sqlean.py` is installed
- Uses `sqlite-dump` if available and `conn.iterdump()` does not exist
- New `with db.ensure_autocommit_off()` method for ensuring autocommit is off, used by `enable_wal()` and `disable_wal()`.

.github/workflows/test.yml

@@ -35,6 +35,9 @@ jobs:
     - name: Install SpatiaLite
       if: matrix.os == 'ubuntu-latest'
       run: sudo apt-get install libsqlite3-mod-spatialite
+    - name: On macOS with Python 3.10 test with sqlean.py
+      if: matrix.os == 'macos-latest' && matrix.python-version == '3.10'
+      run: pip install sqlean.py sqlite-dump
     - name: Build extension for --load-extension test
       if: matrix.os == 'ubuntu-latest'
       run: |-