Replace `src = ./.` instances with more explicit source listings.
Otherwise, derivations will be rebuilt on any change to the files
defining them (e.g. formatting via nixfmt-rfc-style).
In restricted mode (and therefore with flakes) `builtins.readFile` may not be the result of `builtins.toFile`,
making it impossible to use a generated lockFile (with or without IFD),
and thereby causing evaluation to fail if `system != builtins.currentSystem` on Hydra
so the jobs are not delegated to eligible build machines that support that system.
This is done in a way that avoids rebuilds.
jopejoe1