feat(python): add ruff linter and formatter

[alexander-akhmetov]

Add ruff for linting and formatting across all Python SDK packages.
Reformatted the code.

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Note

Low Risk
Mostly introduces Python lint/format tooling (ruff) and applies automated reformatting/type-hint modernizations across Python modules; functional impact should be minimal aside from small refactors like attribute assignment and error-message formatting.

Overview
Adds ruff to the repo toolchain (via mise.toml) with new lint:py and format:py tasks, and wires a dedicated Python Lint job into CI to run ruff check plus ruff format --check.

Applies a broad ruff format pass and related cleanup across Python SDK, providers, frameworks, and tests (import ordering, line wrapping, and modern X | None annotations), with a few tiny refactors such as with_sigil_google_adk_plugins using direct target.plugins = ... assignment and minor error-message string construction tweaks.

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[alexander-akhmetov]

bugbot review

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