Event handling (#5)

- Refactor `event` handling (heavily inspired by [crates-tui](https://github.com/ratatui/crates-tui/) via [Tui with Terminal and EventHandler](https://ratatui.rs/recipes/apps/terminal-and-event-handler/))
- Refactor widget structure
- Disable `nixos-unstable` temporarily
- Add `.rustfmt.toml`

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "crane": {
       "locked": {
-        "lastModified": 1732407143,
-        "narHash": "sha256-qJOGDT6PACoX+GbNH2PPx2ievlmtT1NVeTB80EkRLys=",
+        "lastModified": 1733016477,
+        "narHash": "sha256-Hh0khbqBeCtiNS0SJgqdWrQDem9WlPEc2KF5pAY+st0=",
         "owner": "ipetkov",
         "repo": "crane",
-        "rev": "f2b4b472983817021d9ffb60838b2b36b9376b20",
+        "rev": "76d64e779e2fbaf172110038492343a8c4e29b55",
         "type": "github"
       },
       "original": {
@@ -56,16 +56,16 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1732521221,
-        "narHash": "sha256-2ThgXBUXAE1oFsVATK1ZX9IjPcS4nKFOAjhPNKuiMn0=",
+        "lastModified": 1720535198,
+        "narHash": "sha256-zwVvxrdIzralnSbcpghA92tWu2DV2lwv89xZc8MTrbg=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "4633a7c72337ea8fd23a4f2ba3972865e3ec685d",
+        "rev": "205fd4226592cc83fd4c0885a3e4c9c400efabb5",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-unstable",
+        "ref": "nixos-23.11",
         "repo": "nixpkgs",
         "type": "github"
       }