Fix data races, nil-record panics, scanner SSRF, log date layout, shutdown timeouts, and enable stricter linters (#54)

High (behavioral bugs):
- service.Geo: add RLock on lookups, handle Reload error, keep old DBs on failure
- models.GeoDB.Reload: open new DBs before closing old ones (no reader gap)
- router: guard nil geo records (404 instead of 500) in geo.go, generic.go, dns.go
- router/port_scanner: reject undetermined client IPs (nil->localhost dial)
- internal/httputils: fix access log date layout (02/Jan/2006, not literal Nov)
- server/quic: log.Printf instead of log.Fatal in request handler

Medium:
- server/*: 10s shutdown timeout; SIGTERM drains servers before closing geo DBs
- httputils: Clone() request headers instead of mutating the live map; strings.Builder
- setting/app: handle all os.Stat errors; fix "truster" typos; use errors.New;
  remove dead Token field
- cmd: errors.Is for sentinel checks; os.Stderr; log.Fatal instead of panic;
  pass http.Handler by value (not pointer-to-interface)
- resolver: validate config at startup (pre-parse RRs, validate IPs); check WriteMsg
  errors; Setup returns error

Low:
- .golangci.yaml: enable errcheck, govet, errorlint; fix all resulting findings
- server/tls: explicit TLSConfig{MinVersion: tls.VersionTLS12}
- router/dns: label-exact vhost suffix check, strip port; template.Must
- models: errors.Join instead of %s on []error
- service/geo_test: race-regression test (concurrent lookups during Reload)
- README: Go >= 1.25; fix latent test bug (store.Add->Set in dns_test.go)

internal/httputils/http.go

@@ -11,32 +11,27 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// HeadersToSortedString shorts and dumps http.Header to a string separated by \n
+// HeadersToSortedString sorts and dumps http.Header to a string separated by \n
 func HeadersToSortedString(headers http.Header) string {
-	var output string
-
 	keys := make([]string, 0, len(headers))
 	for k := range headers {
 		keys = append(keys, k)
 	}
 	sort.Strings(keys)
 
+	var output strings.Builder
 	for _, k := range keys {
-		if len(headers[k]) > 1 {
-			for _, h := range headers[k] {
-				output += k + ": " + h + "\n"
-			}
-		} else {
-			output += k + ": " + headers[k][0] + "\n"
+		for _, h := range headers[k] {
+			output.WriteString(k + ": " + h + "\n")
 		}
 	}
 
-	return output
+	return output.String()
 }
 
-// GetHeadersWithoutTrustedHeaders return a http.Heade object with the original headers except trusted headers
+// GetHeadersWithoutTrustedHeaders returns a copy of the request headers with the trusted headers removed
 func GetHeadersWithoutTrustedHeaders(ctx *gin.Context) http.Header {
-	h := ctx.Request.Header
+	h := ctx.Request.Header.Clone()
 
 	for _, k := range []string{setting.App.TrustedHeader, setting.App.TrustedPortHeader} {
 		delete(h, textproto.CanonicalMIMEHeaderKey(k))
@@ -49,7 +44,7 @@ func GetHeadersWithoutTrustedHeaders(ctx *gin.Context) http.Header {
 func GetLogFormatter(param gin.LogFormatterParams) string {
 	return fmt.Sprintf("%s - [%s] \"%s %s %s\" %d %d %d %s \"%s\" \"%s\" \"%s\"\n",
 		param.ClientIP,
-		param.TimeStamp.Format("02/Nov/2006:15:04:05 -0700"),
+		param.TimeStamp.Format("02/Jan/2006:15:04:05 -0700"),
 		param.Method,
 		param.Path,
 		param.Request.Proto,

internal/httputils/http_test.go

@@ -25,7 +25,7 @@ Header3: Three
 }
 
 func TestGetLogFormatter(t *testing.T) {
-	expected := "127.0.0.1 - [01/Nov/0001:00:00:00 +0000] \"GET / HTTP/1.1\" 200 100 1000 local \"golang test 1.0\" \"1.1.1.1, 2.2.2.2\" \"-\"\n"
+	expected := "127.0.0.1 - [15/Jul/2022:10:30:00 +0000] \"GET / HTTP/1.1\" 200 100 1000 local \"golang test 1.0\" \"1.1.1.1, 2.2.2.2\" \"-\"\n"
 
 	h := http.Header{}
 	h.Set("User-Agent", "golang test 1.0")
@@ -39,7 +39,7 @@ func TestGetLogFormatter(t *testing.T) {
 
 	p := gin.LogFormatterParams{
 		ClientIP:     "127.0.0.1",
-		TimeStamp:    time.Time{},
+		TimeStamp:    time.Date(2022, time.July, 15, 10, 30, 0, 0, time.UTC),
 		Method:       "GET",
 		Path:         "/",
 		StatusCode:   200,