Fix the infinite recursion

[UnstoppableMango]

• Fix the thing and also refactor
• Unused param

[Copilot]

Pull request overview

Refactors pkgs/default.nix to avoid self-referential evaluation (the likely source of the “infinite recursion”) by removing the config dependency, lifting packages into a local let binding, and rebuilding overlayAttrs/legacyPackages from that local value.

Changes:

• Refactors callPackage inputs into a tools attrset and uses it to build a shared callPackage.
• Moves packages into a let binding and updates legacyPackages.packagesTable / overlayAttrs to use it (instead of config.packages).
• Switches ocaml-protoc packaging to use ocamlPackages.callPackage (but this currently drops required args; see PR comment).