chore!: drop Python 3.10 support (#908)

## Issue

- Closes: #757

## Summary

- Bump the minimum supported Python to **3.11** in `pyproject.toml`
(`requires-python`, classifiers, `[tool.ty.environment]`) and drop 3.10
from every CI matrix in `.github/workflows/_checks.yaml` (lint,
type-check, unit tests, integration tests, e2e tests).
- Apply ruff autofixes unlocked by the version bump across `src/` and
`tests/`: `UP017` (`datetime.timezone.utc` → `datetime.UTC`), `UP035`
(`typing_extensions.Self` → `typing.Self`), `UP041`
(`asyncio.TimeoutError` → builtin `TimeoutError`).
- Refresh `uv.lock` — the resolver drops the 3.10-only backport packages
(`backports-asyncio-runner`, `exceptiongroup`, `importlib-metadata`,
`zipp`).

## Why

3.10 reaches end-of-life soon, and the upcoming `apify-client` v3
already requires `>=3.11`. Landing the version drop on its own first
keeps the v3 client-upgrade series small and reviewable.

## BREAKING CHANGE

Python 3.10 is no longer supported. Users on 3.10 must upgrade to 3.11+
before pulling the next SDK release.