Update nixpkgs, add direnv to gitignore (#30292)

This also moves nixpkgs to use `channels.nixos.org` since those tarballs
are 30mb in size as compared to 45mb github ones

Release Notes:

- N/A 

----

cc @P1n3appl3

.gitignore

@@ -2,6 +2,7 @@
 **/cargo-target
 **/target
 **/venv
+**/.direnv
 *.wasm
 *.xcodeproj
 .DS_Store

flake.lock

@@ -32,18 +32,15 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1743095683,
+        "lastModified": 315532800,
-        "narHash": "sha256-gWd4urRoLRe8GLVC/3rYRae1h+xfQzt09xOfb0PaHSk=",
+        "narHash": "sha256-kgy4FnRFGj62QO3kI6a6glFl8XUtKMylWGybnVCvycM=",
-        "owner": "NixOS",
+        "rev": "b3582c75c7f21ce0b429898980eddbbf05c68e55",
-        "repo": "nixpkgs",
+        "type": "tarball",
-        "rev": "5e5402ecbcb27af32284d4a62553c019a3a49ea6",
+        "url": "https://releases.nixos.org/nixpkgs/nixpkgs-25.05pre796313.b3582c75c7f2/nixexprs.tar.xz?rev=b3582c75c7f21ce0b429898980eddbbf05c68e55"
-        "type": "github"
       },
       "original": {
-        "owner": "NixOS",
+        "type": "tarball",
-        "ref": "nixos-unstable",
+        "url": "https://channels.nixos.org/nixpkgs-unstable/nixexprs.tar.xz"
-        "repo": "nixpkgs",
-        "type": "github"
       }
     },
     "root": {

flake.nix

@@ -2,7 +2,7 @@
   description = "High-performance, multiplayer code editor from the creators of Atom and Tree-sitter";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs?ref=nixos-unstable";
+    nixpkgs.url = "https://channels.nixos.org/nixpkgs-unstable/nixexprs.tar.xz";
     rust-overlay = {
       url = "github:oxalica/rust-overlay";
       inputs.nixpkgs.follows = "nixpkgs";