Improve Nix package and shell (#21075)

With an addition of useFetchCargoVendor, crane becomes less necessary
for our use. This reuses the package from nixpkgs as well as creating a
better devshell that both work on macOS.

I use Xcode's SDKROOT and DEVELOPER_DIR to point the swift in the
livekit client crate to a correct sdk when using a devshell. Devshell
should work without that once apple releases sources for the 15.1 SDK
but for now this is an easy fix

This also replaces fenix with rust-overlay because of issues with the
out-of-sandbox access I've noticed fenix installed toolchains have

Release Notes:

- N/A

flake.lock

@@ -1,41 +1,5 @@
 {
   "nodes": {
-    "crane": {
-      "locked": {
-        "lastModified": 1727060013,
-        "narHash": "sha256-/fC5YlJy4IoAW9GhkJiwyzk0K/gQd9Qi4rRcoweyG9E=",
-        "owner": "ipetkov",
-        "repo": "crane",
-        "rev": "6b40cc876c929bfe1e3a24bf538ce3b5622646ba",
-        "type": "github"
-      },
-      "original": {
-        "owner": "ipetkov",
-        "repo": "crane",
-        "type": "github"
-      }
-    },
-    "fenix": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs"
-        ],
-        "rust-analyzer-src": "rust-analyzer-src"
-      },
-      "locked": {
-        "lastModified": 1727073227,
-        "narHash": "sha256-1kmkEQmFfGVuPBasqSZrNThqyMDV1SzTalQdRZxtDRs=",
-        "owner": "nix-community",
-        "repo": "fenix",
-        "rev": "88cc292eb3c689073c784d6aecc0edbd47e12881",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-community",
-        "repo": "fenix",
-        "type": "github"
-      }
-    },
     "flake-compat": {
       "locked": {
         "lastModified": 1696426674,
@@ -53,11 +17,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1726937504,
-        "narHash": "sha256-bvGoiQBvponpZh8ClUcmJ6QnsNKw0EMrCQJARK3bI1c=",
+        "lastModified": 1732014248,
+        "narHash": "sha256-y/MEyuJ5oBWrWAic/14LaIr/u5E0wRVzyYsouYY3W6w=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "9357f4f23713673f310988025d9dc261c20e70c6",
+        "rev": "23e89b7da85c3640bbc2173fe04f4bd114342367",
         "type": "github"
       },
       "original": {
@@ -69,26 +33,28 @@
     },
     "root": {
       "inputs": {
-        "crane": "crane",
-        "fenix": "fenix",
         "flake-compat": "flake-compat",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay"
       }
     },
-    "rust-analyzer-src": {
-      "flake": false,
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
       "locked": {
-        "lastModified": 1726443025,
-        "narHash": "sha256-nCmG4NJpwI0IoIlYlwtDwVA49yuspA2E6OhfCOmiArQ=",
-        "owner": "rust-lang",
-        "repo": "rust-analyzer",
-        "rev": "94b526fc86eaa0e90fb4d54a5ba6313aa1e9b269",
+        "lastModified": 1732242723,
+        "narHash": "sha256-NWI8csIK0ujFlFuEXKnoc+7hWoCiEtINK9r48LUUMeU=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "a229311fcb45b88a95fdfa5cecd8349c809a272a",
         "type": "github"
       },
       "original": {
-        "owner": "rust-lang",
-        "ref": "nightly",
-        "repo": "rust-analyzer",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
         "type": "github"
       }
     }