Add unit tests for authentication and webhook parsing

- Implement tests for basic and bearer authentication headers in `test_auth.py`.
- Create tests for the `EasybillWebhookParser` in `test_webhooks.py`, covering JSON and form-encoded payloads, as well as a generic parse and acknowledgement method.

scripts/generate_client.py

@@ -0,0 +1,59 @@
+from __future__ import annotations
+
+import argparse
+import subprocess
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+SPEC = ROOT / "swagger.json"
+OUTPUT_ROOT = ROOT / "generated"
+
+
+def build_command(mode: str) -> list[str]:
+    library = "httpx" if mode == "sync" else "asyncio"
+    package_name = f"easybill_generated_{mode}"
+    project_name = f"easybill-generated-{mode}"
+    output_path = OUTPUT_ROOT / mode
+
+    return [
+        "docker",
+        "run",
+        "--rm",
+        "-v",
+        f"{ROOT}:/local",
+        "openapitools/openapi-generator-cli",
+        "generate",
+        "-i",
+        "/local/swagger.json",
+        "-g",
+        "python",
+        "-o",
+        f"/local/generated/{mode}",
+        "--skip-validate-spec",
+        "--additional-properties",
+        f"library={library},packageName={package_name},projectName={project_name},hideGenerationTimestamp=true",
+    ]
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description="Generate the raw easybill client from swagger.json")
+    parser.add_argument("--mode", choices=["sync", "async", "both"], default="both")
+    args = parser.parse_args()
+
+    if not SPEC.exists():
+        raise SystemExit("swagger.json not found")
+
+    OUTPUT_ROOT.mkdir(exist_ok=True)
+    modes = ["sync", "async"] if args.mode == "both" else [args.mode]
+
+    for mode in modes:
+        command = build_command(mode)
+        print("Running:", " ".join(command))
+        subprocess.run(command, check=True)
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())