Clarify and expand descriptions of `NonFile`s #5341

Job	Run time
test-journey	4m 1s
test-fast (windows-latest)	15m 4s
test-fast (macos-latest)	2m 50s
cargo-deny	27s
lint	3m 48s
test-fast (ubuntu-latest)	3m 43s
cargo-deny-advisories	27s
test-32bit	5m 29s
test-32bit-cross (armv7-linux-androideabi)	1m 5s
test-fixtures-windows	14m 43s
check-blocking	7s
check-packetline (ubuntu-latest)	7s
pure-rust-build	1m 58s
WebAssembly (wasm32-unknown-unknown)	1m 14s
test	10m 3s
WebAssembly (wasm32-wasi)	36s
Tests pass	1s
	1h 5m 43s

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