#6 Add Puzzles.get_batch

[nstillman-te]

Part of #6.

Implements GET /api/puzzle/batch/{angle} as client.puzzles.get_batch(angle, difficulty=..., nb=..., color=...). Adds PuzzleBatchResponse and optional PuzzleUser fields (flair, patron, patronColor). VCR test for response validation and requests_mock test for query params. README.rst and CHANGELOG.rst updated.

Checklist when adding a new endpoint

• Added new endpoint to the README.rst
• Ensured that my endpoint name does not repeat the name of the client. Wrong: client.users.get_user(), Correct: client.users.get()
• Typed the returned JSON using TypedDicts in berserk/types/, example
• Written tests for GET endpoints not requiring authentification. Documentation, example
• Added the endpoint and your name to CHANGELOG.rst in the To be released section (to be created if necessary)