fix: address Rust 1.97 clippy lints - #4074

Summary

• replace the exhausted block iterator match with ?
• remove redundant formatting borrows in the GCP signer and provider filler

Rust 1.97 introduced question_mark and useless_borrows_in_formatting diagnostics that fail the workspace clippy job under -D warnings. These changes preserve behavior while making current main pass the updated stable Clippy checks.