general: add unit tests for >80% coverage

Includes a few minor fixes:
- frontend: support setting port for WHOIS server
- proxy: fix handling of very long lines
- proxy: refactor IP allowlist logic, parse allow IP list at startup

proxy/settings_test.go

@@ -0,0 +1,8 @@
+package main
+
+import "testing"
+
+func TestParseSettings(t *testing.T) {
+	parseSettings()
+	// Good as long as it doesn't panic
+}