Reapply "refactor(nix): nix-filter -> lib.fileset"

After extensive (5 minutes) of testing, it seems we don't actually come
across any Nix bugs with lib.fileset! (aside from those inherit to
it...but 🤷)

This reverts commit a49a58bc4571f87f42f45bb9eeb1a957d5d12331.

Signed-off-by: Seth Flynn <getchoo@tuta.io>

flake.lock

@@ -32,21 +32,6 @@
         "type": "github"
       }
     },
-    "nix-filter": {
-      "locked": {
-        "lastModified": 1731533336,
-        "narHash": "sha256-oRam5PS1vcrr5UPgALW0eo1m/5/pls27Z/pabHNy2Ms=",
-        "owner": "numtide",
-        "repo": "nix-filter",
-        "rev": "f7653272fd234696ae94229839a99b73c9ab7de0",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "nix-filter",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1743095683,
@@ -67,7 +52,6 @@
       "inputs": {
         "flake-compat": "flake-compat",
         "libnbtplusplus": "libnbtplusplus",
-        "nix-filter": "nix-filter",
         "nixpkgs": "nixpkgs"
       }
     }

flake.nix

@@ -16,8 +16,6 @@
       flake = false;
     };
 
-    nix-filter.url = "github:numtide/nix-filter";
-
     /*
       Inputs below this are optional and can be removed
 
@@ -44,7 +42,6 @@
       self,
       nixpkgs,
       libnbtplusplus,
-      nix-filter,
       ...
     }:
     let
@@ -100,7 +97,6 @@
         prismlauncher-unwrapped = prev.callPackage ./nix/unwrapped.nix {
           inherit
             libnbtplusplus
-            nix-filter
             self
             ;
         };

nix/unwrapped.nix

@@ -11,7 +11,6 @@
   kdePackages,
   libnbtplusplus,
   ninja,
-  nix-filter,
   self,
   stripJavaArchivesHook,
   tomlplusplus,
@@ -29,17 +28,18 @@ stdenv.mkDerivation {
   pname = "prismlauncher-unwrapped";
   version = self.shortRev or self.dirtyShortRev or "unknown";
 
-  src = nix-filter.lib {
-    root = self;
-    include = [
-      "buildconfig"
-      "cmake"
-      "launcher"
-      "libraries"
-      "program_info"
-      "tests"
-      ../COPYING.md
+  src = lib.fileset.toSource {
+    root = ../.;
+    fileset = lib.fileset.unions [
       ../CMakeLists.txt
+      ../COPYING.md
+
+      ../buildconfig
+      ../cmake
+      ../launcher
+      ../libraries
+      ../program_info
+      ../tests
     ];
   };