racket: add package system support

[rc-zb]

Follows #375992.
Integrate the package system of Racket with Nixpkgs.

TODOs

1. Pass racket-test.
   Current problems:
   • Fail to write to $out/share/doc/racket/acks/blueboxes.rktd
2. Build the full distribution upon racket-minimal and the package system.
3. Add more packages.

Limitations

• To reduce time & space and gain power from the substitutes, it would be best if each Racket package were built separately like most of other packages in Nixpkgs. However, circular dependence, which is illegal for Nix early in evaluation time but accepted by Racket as long as they does not actually reference mutually in the code level (and for docs, even code level circles are allowed), is so common among these packages. As a result, racket.makePackage in this PR merely re-packs the original package into some canonical places, and it's the end user oriented racket.buildPackages and its tethered variant racket.withPackages that actually build them.
• The layered installation mechanism of Racket is integrated with the package build system. However, since we can't get the complete list of transitive dependencies inside stdenv, only direct dependencies specified as buildInputs, depsHostHost and their propagated variants are included as layers.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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