move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/tdsync/cancel_group.go

@@ -0,0 +1,63 @@
+// Package tdsync contains some useful synchronization utilities.
+package tdsync
+
+import (
+	"context"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// CancellableGroup is simple wrapper around
+// errgroup.Group to make group cancellation easier.
+// Unlike WaitGroup and errgroup.Group this is not allowed to use zero value.
+type CancellableGroup struct {
+	cancel context.CancelFunc
+
+	group *errgroup.Group
+	ctx   context.Context
+}
+
+// NewCancellableGroup creates new CancellableGroup.
+//
+// Example:
+//
+//	g := NewCancellableGroup(ctx)
+//	g.Go(func(ctx context.Context) error {
+//		<-ctx.Done()
+//		return ctx.Err()
+//	})
+//	g.Cancel()
+//	g.Wait()
+func NewCancellableGroup(parent context.Context) *CancellableGroup {
+	ctx, cancel := context.WithCancel(parent)
+	group, groupCtx := errgroup.WithContext(ctx)
+
+	return &CancellableGroup{
+		cancel: cancel,
+		group:  group,
+		ctx:    groupCtx,
+	}
+}
+
+// Go calls the given function in a new goroutine.
+//
+// The first call to return a non-nil error cancels the group; its error will be
+// returned by Wait.
+func (g *CancellableGroup) Go(f func(ctx context.Context) error) {
+	g.group.Go(func() error {
+		return f(g.ctx)
+	})
+}
+
+// Cancel cancels all goroutines in group.
+//
+// Note: context cancellation error will be returned by Wait().
+func (g *CancellableGroup) Cancel() {
+	g.cancel()
+}
+
+// Wait blocks until all function calls from the Go method have returned, then
+// returns the first non-nil error (if any) from them.
+func (g *CancellableGroup) Wait() error {
+	return g.group.Wait()
+}