feat: add Yandex SmartCaptcha image example - #19

Summary

• add sync and async examples for image-based Yandex SmartCaptcha
• bundle the supplied captcha and instruction images
• document that Yandex image challenges use CoordinatesTask
• cover imgInstructions serialization

Verification

• python -m pytest -q (82 passed)
• python -m compileall -q captcha_solver_api examples tests
• live API solve returned four ordered coordinates

Packaging

• build could not run in the managed environment because temporary build directories were denied access
• twine is not installed in the environment