pre-commit: optimise local hook triggers

* rm 'require_serial = false' occurences as that's the default value,
  which makes it redundant here.
* do not "always_run" hooks
* only run relevant local hooks when pertaining files/file groups have
  changed, e.g. there is no need to run statix linter when no nix files
  have changed or equally it is not necessary to run 'nix build' when
  none of the flake files (flake.{nix,lock}), any '*.nix' or go source,
  mod or sum files have changed.
  all of the above results in much faster pre-commit runs, i.e. shorter
  feedback loops, i.e. faster iteration cycles.

.pre-commit-config.yaml

@@ -16,23 +16,25 @@ repos:
       - id: statix
         name: statix
         entry: statix check .
+        always_run: false
         pass_filenames: false
+        files: '\.*.nix$'
         language: system
       - id: nixpkgs-fmt
-        require_serial: false
         name: nixpkgs-fmt
         entry: ./check-fmt
+        always_run: false
         pass_filenames: false
+        files: '\.*.nix$'
         language: system
       - id: flake-check
-        require_serial: false
         name: nix flake check
         entry: nix flake check --impure
+        always_run: false
         pass_filenames: false
-        files: "flake.nix"
+        files: "flake.(nix|lock)$"
         language: system
       - id: addlicense
-        require_serial: false
         name: addlicence -check
         entry: >
           go run github.com/google/addlicense@v1.0.0 -check -v
@@ -63,4 +65,7 @@ repos:
         name: nix build
         entry: nix build .#go-xkcdreader
         pass_filenames: false
+        # trigger this hook on changes to any of nix (also flake.lock) files
+        # and go's src, mod or sum files
+        files: '\.*.(nix|lock|go|mod|sum)$'
         language: system