yarr: use pre-built binary instead of building from source

Building yarr from source (Rust) takes ~5+ min and times out the
config-nixos CI runner (3h limit) when combined with the full
perlis+wilkes+relay flake check. Use the pre-built x86_64-linux binary
from GitHub releases instead — fast fetch, no Rust toolchain needed.

Removes the rust-nixpkgs flake input (no longer needed).

packages/default.nix

@@ -1,4 +1,4 @@
-{ pkgs, rustPkgs ? pkgs }:
+{ pkgs }:
 
 {
   manim-mcp-server = pkgs.callPackage ./manim-mcp-server/package.nix { };
@@ -28,6 +28,6 @@
   navidrome-mcp = pkgs.callPackage ./navidrome-mcp/package.nix { };
   ovhcloud-mcp = pkgs.callPackage ./ovhcloud-mcp/package.nix { };
   slskd-mcp = pkgs.callPackage ./slskd-mcp/package.nix { };
-  yarr = rustPkgs.callPackage ./yarr/package.nix { };
+  yarr = pkgs.callPackage ./yarr/package.nix { };
   # example-mcp-server = pkgs.callPackage ./example-mcp-server/package.nix { };
 }