Quoted commands aren’t recognized as being parallelizable

Example: `"cat" "$0" | "tr" "A-Z" "a-z"` isn’t parallelizable, but `cat $0 | tr A-Z a-z` is. Not a common scenario, but should be a simple fix (unless this is intended).

No file or test is named in the issue. Reproduce the two pipeline examples and trace the entry point that decides whether a command is parallelizable; done means the quoted and unquoted forms are treated consistently, with coverage for both examples.

Written by the indexing model from the issue text.