chore(flake): refresh nixpkgs inputs to 2026-09-11

Bump nixpkgs and nixpkgs-latest from 2026-05/2026-08 to current
nixos-unstable (2026-09-11); both inputs now resolve to the same rev.
Re-validated every package against the new inputs.

Fallout fixed:
- freetoken: upstream pins torch>=2.11,<2.12 and triton==3.6.0, but the new
  nixpkgs only ships torch 2.13 / triton 3.7. Add a nixpkgs-torch211 input
  pinned at the previous revision and build freetoken against it, keeping
  the CUDA 12.9 / torch 2.11 stack unchanged.
- graphify: nixpkgs' pybloomfilter3 0.7.3 ships sdist metadata that still
  says 0.7.2, tripping pythonMetadataCheckPhase; skip that check only.

All 22 packages build and `nix flake check --no-build` passes.

packages/graphify/default.nix

@@ -2,4 +2,18 @@
   pkgs,
   ...
 }:
-pkgs.callPackage ./package.nix { }
+# nixpkgs' pybloomfilter3 0.7.3 (a datasketch dependency) ships sdist metadata
+# that still says 0.7.2, which makes pythonMetadataCheckPhase fail even though
+# the build succeeds. Skip only that check.
+let
+  python = pkgs.python3.override {
+    packageOverrides = self: super: {
+      pybloomfilter3 = super.pybloomfilter3.overridePythonAttrs (_: {
+        dontCheckPythonMetadata = true;
+      });
+    };
+  };
+in
+python.pkgs.callPackage ./package.nix {
+  python3Packages = python.pkgs;
+}