feature: Type annotations and mypy support

[LuckySting]

Feature Request

Describe the Feature Request

Modern python projects use Mypy to do a static type checking. It allows to avoid many problems and make the development process faster and easier. Mypy requires library to be PEP 561 compatible.

Describe Preferred Solution

Configure Mypy type check for this repository and add all PEP 561 required files and stubs.

Describe Alternatives

Another solution is to create a separate ydb-stubs repository only with stubs (*.pyi files).

If the feature request is approved, would you be willing to submit a PR? No