fix(python): expose cursor write statistics

[sundy-li]

Summary

• preserve ServerStats from the blocking cursor query stream instead of dropping stats events
• report write_progress.rows through DB-API cursor.rowcount
• expose the latest server statistics through cursor.stats
• keep executemany rowcount/statistics consistent with execute
• cover SELECT, INSERT, UPDATE, REPLACE, and stream-load cursor behavior

Closes #790.

Verification

• cargo fmt --all -- --check
• cargo check -p databend-python
• cargo test -p databend-python --lib
• cd bindings/python && uv run ruff format --check package/databend_driver/__init__.pyi tests/cursor/steps/binding.py
• git diff --check

Not Run

• make integration-bindings-python was attempted, but Docker could not pull images because the daemon proxy points to unavailable 127.0.0.1:1090.
• cargo clippy -p databend-python --all-targets --all-features -- -D warnings was attempted, but it fails on the pre-existing unused chrono::FixedOffset import in bindings/python/src/types.rs.