build: enable goimports and varcheck linters (#16446)

build/goimports.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+find_files() {
+  find . -not \( \
+      \( \
+        -wholename '.github' \
+        -o -wholename './build/_workspace' \
+        -o -wholename './build/bin' \
+        -o -wholename './crypto/bn256' \
+        -o -wholename '*/vendor/*' \
+      \) -prune \
+    \) -name '*.go'
+}
+
+GOFMT="gofmt -s -w";
+GOIMPORTS="goimports -w";
+find_files | xargs $GOFMT;
+find_files | xargs $GOIMPORTS;