Fix lint errors and bump golangci-lint to v2/action v9

- Migrate .golangci.yml to golangci-lint v2 config format
- Bump golangci-lint-action from v6 (Node 20, deprecated) to v9 (Node 24)
- Fix errcheck: check fmt.Fscanln and fmt.Sscanf return values
- Fix ineffassign: replace unused vars with _ in test files
- Fix revive unused-parameter: rename unused cmd/args/r/c params to _
- Fix revive empty-block: invert if condition in push command
- Fix revive redefines-builtin-id: rename 'clear' to 'clearsigned'
- Fix revive blank-imports: add comment on modernc.org/sqlite import
- Fix unused: remove unused 'suite' and 'gen' fields from cache entry

.golangci.yml

@@ -1,21 +1,36 @@
+version: "2"
 run:
-  timeout: 5m
-  go: "1.22"
-
+  go: "1.26"
 linters:
-  disable-all: true
+  default: none
   enable:
     - errcheck
     - govet
     - ineffassign
-    - staticcheck
-    - unused
     - misspell
     - revive
-
-issues:
-  exclude-rules:
-    - path: _test\.go
-      linters:
-        - errcheck
-        - revive
+    - staticcheck
+    - unused
+  exclusions:
+    generated: lax
+    presets:
+      - comments
+      - common-false-positives
+      - legacy
+      - std-error-handling
+    rules:
+      - linters:
+          - errcheck
+          - revive
+        path: _test\.go
+    paths:
+      - third_party$
+      - builtin$
+      - examples$
+formatters:
+  exclusions:
+    generated: lax
+    paths:
+      - third_party$
+      - builtin$
+      - examples$