Review clippy configuration and address warnings as appropriate #555
Description
Our clippy allow/deny list is a bit dated (and in particular, it predates the ability to specify the lint levels in Cargo.toml, which is preferable to doing so in lib.rs). We have at least one performance-oriented list, result_large_error, that we should fix in the code, but which is currently configured as a warning. We should review the configuration, move it into Cargo.toml, and apply code fixes where appropriate.