ci: build the bot in nix in order to cache it early on

.gitlab-ci.yml

@@ -10,6 +10,10 @@ stages:
 variables:
   RUST_BACKTRACE: FULL
 
+.scripts_cache: &scripts_cache
+  - nix --extra-experimental-features 'nix-command flakes'  profile install nixpkgs#attic-client
+  - attic login skynet https://nix-cache.skynet.ie/ $CACHE_KEY
+  - attic use skynet-cache
 
 # clippy and fmt are magic
 # runs on all commits/branches
@@ -20,6 +24,7 @@ lint-clippy:
     - rustc --version
     - cargo version
     - cargo clippy
+    - cargo test --verbose
   rules:
     - if: $CI_COMMIT_TAG
       when: never
@@ -47,11 +52,13 @@ lint-fmt:
 # has to actually compile
 build:
   stage: build
+  tags:
+    - nix
+  before_script:
+    - *scripts_cache
   script:
-    - rustc --version
+    - attic watch-store skynet-cache &
-    - cargo version
+    - nix build --verbose
-    - cargo build --verbose
-    - RUST_BACKTRACE=1 cargo test --verbose
   rules:
     - if: $CI_COMMIT_TAG
       when: never