pacquet: drop the vestigial `Fn() -> DependencyGroupList` generic from `Add`

Context

pacquet_package_manager::Add (pnpm/crates/package-manager/src/add.rs) is generic over two parameters:

pub struct Add<'a, ListDependencyGroups, DependencyGroupList>
where
    ListDependencyGroups: Fn() -> DependencyGroupList,
    DependencyGroupList: IntoIterator<Item = DependencyGroup>,

The closure existed because the list was consumed more than once. The field used to say so:

pub list_dependency_groups: ListDependencyGroups, // must be a function because it is called multiple times

https://github.com/pnpm/pnpm/pull/12995 changed that. Add::run now collects the groups once and reuses the Vec:

let dependency_groups: Vec<DependencyGroup> = list_dependency_groups().into_iter().collect();

That PR correctly deleted the now-false comment, but left the machinery behind. list_dependency_groups is called exactly once, so the Fn() indirection no longer buys anything — a reader of the struct now sees a generic closure parameter with no justification.

Proposal

Collapse to a single generic and take the groups directly:

pub struct Add<'a, DependencyGroupList>
where
    DependencyGroupList: IntoIterator<Item = DependencyGroup>,
{
    pub dependency_groups: DependencyGroupList,
    // ...
}

and thread dependency_groups: impl IntoIterator<Item = DependencyGroup> through add_package / add_packages in pnpm/crates/cli/src/cli_args/add.rs.

Every call site currently passes a trivial closure, so each becomes marginally simpler:

Call site	Now	After
cli_args/add.rs	|| self.dependency_options.dependency_groups()	self.dependency_options.dependency_groups()
cli_args/global.rs	|| std::iter::once(DependencyGroup::Prod)	[DependencyGroup::Prod]
cli_args/dlx.rs	|| std::iter::once(DependencyGroup::Prod)	[DependencyGroup::Prod]
cli_args/runtime.rs	|| std::iter::once(request.dependency_group)	[request.dependency_group]
cli_args/self_update/install_pnpm.rs	|| std::iter::once(DependencyGroup::Prod)	[DependencyGroup::Prod]

Notes

Pure refactor — no user-visible behavior changes, so no changeset and no TypeScript counterpart. It was left out of https://github.com/pnpm/pnpm/pull/12995 under the scope-discipline rule in REVIEW_GUIDE.md §4, since it reaches three files (dlx.rs, runtime.rs, install_pnpm.rs) that PR otherwise had no reason to touch.

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Written by an agent (Claude Code, claude-opus-4-8).