doc: add function argument order convention (#110060)

* doc: add function argument order convention

Ordering by usage is the de facto ordering given to arguments. It's
logical, and makes finding argument usage easier. Putting lib first is
common in NixOS modules, so it's reasonable to mirror this in nixpkgs
proper. Additionally, it's not a package as such, has zero dependencies,
and can be found used anywhere in a derivation.

* doc: clean up usage of lib

doc/languages-frameworks/rust.section.md

@@ -19,6 +19,8 @@ or use Mozilla's [Rust nightlies overlay](#using-the-rust-nightlies-overlay).
 Rust applications are packaged by using the `buildRustPackage` helper from `rustPlatform`:
 
 ```
+{ lib, rustPlatform }:
+
 rustPlatform.buildRustPackage rec {
   pname = "ripgrep";
   version = "12.1.1";
@@ -226,8 +228,6 @@ source code in a reproducible way. If it is missing or out-of-date one can use
 the `cargoPatches` attribute to update or add it.
 
 ```
-{ lib, rustPlatform, fetchFromGitHub }:
-
 rustPlatform.buildRustPackage rec {
   (...)
   cargoPatches = [
@@ -263,7 +263,7 @@ Now, the file produced by the call to `carnix`, called `hello.nix`, looks like:
 
 ```
 # Generated by carnix 0.6.5: carnix -o hello.nix --src ./. Cargo.lock --standalone
-{ lib, stdenv, buildRustCrate, fetchgit }:
+{ stdenv, buildRustCrate, fetchgit }:
 let kernel = stdenv.buildPlatform.parsed.kernel.name;
     # ... (content skipped)
 in
@@ -292,7 +292,7 @@ following nix file:
 
 ```
 # Generated by carnix 0.6.5: carnix -o hello.nix --src ./. Cargo.lock --standalone
-{ lib, stdenv, buildRustCrate, fetchgit }:
+{ stdenv, buildRustCrate, fetchgit }:
 let kernel = stdenv.buildPlatform.parsed.kernel.name;
     # ... (content skipped)
 in