fix: update .golangci.yml to v2 config format

golangci-lint v2 requires version: "2" at the top level, linters.settings
(not linters-settings), and issues.exclusions.rules (not issues.exclude-rules).
Also removed gosimple and unused which are now merged into staticcheck.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.golangci.yml

@@ -1,24 +1,23 @@
+version: "2"
+
 linters:
   enable:
     - errcheck
     - govet
     - staticcheck
-    - gosimple
     - ineffassign
-    - unused
     - errorlint
     - gocritic
     - revive
-
-linters-settings:
+  settings:
     revive:
       rules:
         - name: exported
           disabled: true
 
 issues:
-  exclude-rules:
-    # Test files can use dot-imports and assertion helpers freely
+  exclusions:
+    rules:
       - path: _test\.go
         linters:
           - errcheck