Client library performance

Most of pyiceberg's latency gap with the Rust Iceberg client sits in Python's HTTP library

Rust's Iceberg REST client ran up to 4.29x faster than pyiceberg on a local catalog, with 85% to 90% of the gap in Python's HTTP library. pyiceberg covers 21 of 25 tested endpoints to Rust's 13, so coverage settles the choice before speed does.