refactor(handler/tunnel): code review fixes and entrypoint subpackage extraction

- Fix dead-code branch in bind.go host assignment (always use endpoint hash)
- Return descriptive error on bypass match in connect.go (was masking as success)
- Update bypass test in connect_test.go for new error behavior
- Extract entrypoint subpackage from monolithic entrypoint.go (6 files)
- Fix observeStats event-loss bug (break -> fallthrough on retry success)
- Add 47 unit tests across handler, connect, bind, metadata packages
- Add architecture doc comments to all key files
- Build and vet clean, 173 tests pass with -race

handler/tunnel/helpers_test.go

@@ -1,9 +1,18 @@
 package tunnel
 
 import (
+	"os"
+	"testing"
+
 	"github.com/go-gost/core/logger"
 )
 
+// TestMain sets up a non-nil default logger for all tests in this package.
+func TestMain(m *testing.M) {
+	logger.SetDefault(nopLogger{})
+	os.Exit(m.Run())
+}
+
 type nopLogger struct {
 	logger.Logger
 }