Importing <nixpkgs> tied extraction to the caller's NIX_PATH. When that
channel lacks a maintainer referenced through `with lib.maintainers`
(such as sherlock's `_74k1`, which exists in the locked nixpkgs but not
in an older channel), evaluation fails outright and the generated list
varies by machine. Resolve nixpkgs from flake.lock so extraction matches
what Home Manager builds with.
Also classify maintainers by identity (github/name) rather than attribute
name so renamed entries like `_9p4` still match, and correct the
arguments passed to the manual derivation so its maintainer is collected.
Austin Horstman
7042d2b31b