nix: add cargo-nextest to default devshell

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Ica8a3f57f6b005134be2ade63bdfe9746a6a6964

nix/shell.nix

@@ -2,10 +2,11 @@
   mkShell,
   rustc,
   cargo,
-  rust-analyzer-unwrapped,
   rustfmt,
   clippy,
   taplo,
+  rust-analyzer-unwrapped,
+  cargo-nextest,
   rustPlatform,
 }:
 mkShell {
@@ -24,6 +25,9 @@ mkShell {
 
     # LSP
     rust-analyzer-unwrapped
+
+    # Additional Cargo tooling
+    cargo-nextest
   ];
 
   env.RUST_SRC_PATH = "${rustPlatform.rustLibSrc}";