checks/inventory: optimize eval tests to use filtered sources

Replace full flake source (self) with minimal filtered filesets to prevent
unnecessary rebuilds when unrelated files change. All three inventory eval
tests now use the same unified fileset containing only necessary files.

This follows the same optimization pattern applied to other eval tests,
significantly reducing rebuild frequency during development.

lib/modules/inventory/distributed-service/flake-module.nix

@@ -10,6 +10,23 @@ in
       system,
       ...
     }:
+    let
+      # Common filtered source for inventory tests
+      inventoryTestsSrc = lib.fileset.toSource {
+        root = ../../../..;
+        fileset = lib.fileset.unions [
+          ../../../../flake.nix
+          ../../../../flake.lock
+          (lib.fileset.fileFilter (file: file.name == "flake-module.nix") ../../../..)
+          ../../../../flakeModules
+          ../../../../lib
+          ../../../../nixosModules/clanCore
+          ../../../../clanModules/borgbackup
+          ../../../../machines
+          ../../../../inventory.json
+        ];
+      };
+    in
     {
       # Run: nix-unit --extra-experimental-features flakes --flake .#legacyPackages.x86_64-linux.<attrName>
       legacyPackages.evalTests-distributedServices = import ./tests {
@@ -27,7 +44,7 @@ in
             --extra-experimental-features flakes \
             --show-trace \
             ${inputOverrides} \
-            --flake ${self}#legacyPackages.${system}.evalTests-distributedServices
+            --flake ${inventoryTestsSrc}#legacyPackages.${system}.evalTests-distributedServices
 
           touch $out
         '';
@@ -37,7 +54,7 @@ in
             --extra-experimental-features flakes \
             --show-trace \
             ${inputOverrides} \
-            --flake ${self}#legacyPackages.${system}.eval-tests-resolve-module
+            --flake ${inventoryTestsSrc}#legacyPackages.${system}.eval-tests-resolve-module
 
           touch $out
         '';

lib/modules/inventory/flake-module.nix

@@ -68,12 +68,18 @@ in
             --show-trace \
             ${inputOverrides} \
             --flake ${
-              self.filter {
-                include = [
-                  "flakeModules"
-                  "lib"
-                  "clanModules/flake-module.nix"
-                  "clanModules/borgbackup"
+              lib.fileset.toSource {
+                root = ../../..;
+                fileset = lib.fileset.unions [
+                  ../../../flake.nix
+                  ../../../flake.lock
+                  (lib.fileset.fileFilter (file: file.name == "flake-module.nix") ../../..)
+                  ../../../flakeModules
+                  ../../../lib
+                  ../../../nixosModules/clanCore
+                  ../../../clanModules/borgbackup
+                  ../../../machines
+                  ../../../inventory.json
                 ];
               }
             }#legacyPackages.${system}.evalTests-inventory