flake.lock: Update

Flake lock file updates:

```
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/a684c58d46ebbede49f280b653b9e56100aa3877' (2025-06-27)
  → 'github:nixos/nixpkgs/50ab793786d9de88ee30ec4e4c24fb4236fc2674' (2025-06-30)
• Updated input 'nixpkgs-unstable':
    'github:nixos/nixpkgs/30e2e2857ba47844aa71991daa6ed1fc678bcbb7' (2025-06-27)
  → 'github:nixos/nixpkgs/6e987485eb2c77e5dcc5af4e3c70843711ef9251' (2025-07-16)
• Updated input 'treefmt-nix':
    'github:numtide/treefmt-nix/ac8e6f32e11e9c7f153823abc3ab007f2a65d3e1' (2025-06-26)
  → 'github:numtide/treefmt-nix/0043b95d80b5bf6d61e84d237e2007727f4dd38d' (2025-07-19)
```

flake.lock

@@ -36,11 +36,11 @@
     },
     "nixpkgs-unstable": {
       "locked": {
-        "lastModified": 1752480373,
-        "narHash": "sha256-JHQbm+OcGp32wAsXTE/FLYGNpb+4GLi5oTvCxwSoBOA=",
+        "lastModified": 1752687322,
+        "narHash": "sha256-RKwfXA4OZROjBTQAl9WOZQFm7L8Bo93FQwSJpAiSRvo=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "62e0f05ede1da0d54515d4ea8ce9c733f12d9f08",
+        "rev": "6e987485eb2c77e5dcc5af4e3c70843711ef9251",
         "type": "github"
       },
       "original": {
@@ -95,11 +95,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1752055615,
-        "narHash": "sha256-19m7P4O/Aw/6+CzncWMAJu89JaKeMh3aMle1CNQSIwM=",
+        "lastModified": 1752909129,
+        "narHash": "sha256-Eh8FkMvGRaY71BU/oyZTTzt9RsBIq2E6j0r3eLZ/2kY=",
         "owner": "numtide",
         "repo": "treefmt-nix",
-        "rev": "c9d477b5d5bd7f26adddd3f96cfd6a904768d4f9",
+        "rev": "0043b95d80b5bf6d61e84d237e2007727f4dd38d",
         "type": "github"
       },
       "original": {