Preserve context in With() calls (#17)

Currently `With()` will reset context back to `context.Background()`,
causing the `wrap/wrapf` calls to lose the original context.

This affects the `clog/gcp` handler who relies on a value keyed with
`"trace"` being set on the context
([see](https://github.com/chainguard-dev/clog/blob/main/gcp/trace.go#L110-L116))
(we should use a typed value though, but that's in a different PR).

---------

Signed-off-by: Nghia Tran <tcnghia@gmail.com>

logger.go

@@ -53,12 +53,12 @@ func With(args ...any) *Logger {
 
 // With calls [Logger.With] on the logger.
 func (l *Logger) With(args ...any) *Logger {
-	return NewLogger(l.Logger.With(args...))
+	return NewLoggerWithContext(l.context(), l.Logger.With(args...))
 }
 
 // WithGroup calls [Logger.WithGroup] on the default logger.
 func (l *Logger) WithGroup(name string) *Logger {
-	return NewLogger(l.Logger.WithGroup(name))
+	return NewLoggerWithContext(l.context(), l.Logger.WithGroup(name))
 }
 
 func (l *Logger) context() context.Context {

logger_test.go

@@ -113,3 +113,16 @@ func TestLoggerPC(t *testing.T) {
 		t.Errorf("want %v, got %v", want, got)
 	}
 }
+
+func TestWith(t *testing.T) {
+	ctx := context.WithValue(context.Background(), "test", "test")
+	log := NewLoggerWithContext(ctx, nil)
+	withed := log.With("a", "b")
+	if want := withed.ctx; want != ctx {
+		t.Errorf("want %v, got %v", want, ctx)
+	}
+	withed = log.WithGroup("a")
+	if want := withed.ctx; want != ctx {
+		t.Errorf("want %v, got %v", want, ctx)
+	}
+}