fix(dialer): correct inverted setMark on FreeBSD/OpenBSD

Fix setMark early-return conditions that were inverted relative to
Linux: on FreeBSD (SO_USER_COOKIE) and OpenBSD (SO_RTABLE), a
non-zero mark was short-circuited instead of applied, disabling
socket marking entirely.

Also fix GetClientIP to trim leading whitespace from X-Forwarded-For
entries (per RFC 7239), and fix Body.Read to subtract len(b) instead
of n from recordSize when a single read exceeds the remaining quota.

Add unit tests for internal/net/ (addr, dialer, http, ip, net, pipe,
transport, resolve, proxyproto, udp).

internal/net/dialer/main_test.go

@@ -0,0 +1,31 @@
+package dialer
+
+import (
+	"os"
+	"testing"
+
+	"github.com/go-gost/core/logger"
+)
+
+type nopLogger struct{}
+
+func (l *nopLogger) WithFields(map[string]any) logger.Logger      { return l }
+func (l *nopLogger) Trace(args ...any)                             {}
+func (l *nopLogger) Tracef(format string, args ...any)             {}
+func (l *nopLogger) Debug(args ...any)                             {}
+func (l *nopLogger) Debugf(format string, args ...any)             {}
+func (l *nopLogger) Info(args ...any)                              {}
+func (l *nopLogger) Infof(format string, args ...any)              {}
+func (l *nopLogger) Warn(args ...any)                              {}
+func (l *nopLogger) Warnf(format string, args ...any)              {}
+func (l *nopLogger) Error(args ...any)                             {}
+func (l *nopLogger) Errorf(format string, args ...any)             {}
+func (l *nopLogger) Fatal(args ...any)                             {}
+func (l *nopLogger) Fatalf(format string, args ...any)             {}
+func (l *nopLogger) GetLevel() logger.LogLevel                     { return logger.InfoLevel }
+func (l *nopLogger) IsLevelEnabled(level logger.LogLevel) bool     { return false }
+
+func TestMain(m *testing.M) {
+	logger.SetDefault(&nopLogger{})
+	os.Exit(m.Run())
+}