Update shellFor documentation

[hamishmack]

Fixes #2401

[Copilot]

Pull Request Overview

This PR updates the documentation and a module description for the shellFor feature, and records the change in the changelog.

• Fix a typo in the modules/shell.nix description for the allToolDeps default behavior.
• Expand the shellFor argument table in docs/reference/library.md, adding new options and usage examples.
• Add a changelog entry to explain the new argument validation for shellFor.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
modules/shell.nix	Corrected typo in description of allToolDeps default value.
docs/reference/library.md	Added and reorganized shellFor table entries; included examples.
changelog.md	Documented the updated shellFor argument validation behavior.

Comments suppressed due to low confidence (3)

docs/reference/library.md:446

• The Type column for buildInputs is empty in the table. Consider specifying its type (e.g., List or AttrSet).

| `buildInputs`  | | Passed to [`mkDerivation`](https://nixos.org/nixpkgs/manual/#sec-using-stdenv) (via [mkShell](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-mkShell)). |

docs/reference/library.md:447

• The Type column for nativeBuildInputs is empty in the table. Consider specifying its type (e.g., List or AttrSet).

| `nativeBuildInputs` | | Passed to [`mkDerivation`](https://nixos.org/nixpkgs/manual/#sec-using-stdenv) (via [mkShell](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-mkShell)). |

docs/reference/library.md:448

• The Type column for passthru is empty in the table. Consider specifying its type (e.g., AttrSet).

| `passthru`     | | Passed to [`mkDerivation`](https://nixos.org/nixpkgs/manual/#sec-using-stdenv)  (via [mkShell](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-mkShell)). |