Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@nix/module.nix`:
- Around line 193-198: The doas rule is producing duplicate SSH_AUTH_SOCK
entries because the module unconditionally prepends "SSH_AUTH_SOCK TERMINFO
TERMINFO_DIRS" while you also pass cfg.preserve-env into setEnv; update the
assignment used in security.doas.extraRules so the preserved-env list explicitly
removes the unconditional SSH_AUTH_SOCK before passing it to setEnv (e.g.
prepend "-SSH_AUTH_SOCK" or otherwise filter cfg.preserve-env) so the final
setEnv for the rule does not contain SSH_AUTH_SOCK twice.
- Around line 138-152: The description incorrectly references a non-existent
nested attribute `options.services.nixos-cli.preserve-env.options`; update the
text to point to the correct attribute `services.nixos-cli.preserve-env` (or
`options.services.nixos-cli.preserve-env` if referring to the evaluated option
path) so users look up the list value correctly; locate the paragraph mentioning
`options.services.nixos-cli.preserve-env.options` and replace that token with
`services.nixos-cli.preserve-env` and adjust surrounding wording if needed to
reflect that `preserve-env` is a list of strings.
- Around line 115-124: The option-cache.exclude mkOption lacks a type and
default which causes evaluation failures when cfg.option-cache.exclude is
referenced; update the lib.mkOption for option-cache.exclude to set an explicit
type (e.g. a list type such as types.listOf types.str or appropriate
attr-path/list type consistent with removeNestedAttrs usage) and add default =
[] so cfg.option-cache.exclude is defined by default; ensure this change aligns
with option-cache.enable behavior and prevents lib.foldl' in removeNestedAttrs
from receiving a non-list.