clippy: fix errors introduced with Rust 1.84

[cakebaker]

This PR fixes a bunch of clippy errors introduced with Rust 1.84:

• an error from unnecessary_map_or in cp
• two errors from regex_creation_in_loops in ls tests
• an error from large_stack_arrays in a cp test

It also allows the large_stack_arrays lint in Cargo.toml because the lint only partially works (see rust-lang/rust-clippy#13774)

[cakebaker]

Changes since last push:

• fixed two additional errors from the unnecessary_map_or lint on macOS and Windows

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)