Regular Sync - First Pass (#3201)

* checkpoint

* checkpoint

* varint prefix for ssz

* move the encoding API around a little bit to support reader writer

* add a simple test for the happy path subscribe

* move wait timeout to testutil

* Add inverted topic mapping

* Add varint prefixing to ssz network encoder

* fix spacing

* fix comments

* fix comments

* make anon methods more clear

* clean up log fields

* move topic mapping, reformat TODOs, get ready for brutal team review

* lint

* lint

* lint

* Update beacon-chain/p2p/gossip_topic_mappings.go

Co-Authored-By: Nishant Das <nishdas93@gmail.com>

* PR feedback

* PR feedback

* PR feedback

* PR feedback

* PR feedback

* Update WORKSPACE

* Update WORKSPACE

shared/testutil/BUILD.bazel

@@ -10,6 +10,7 @@ go_library(
         "json_to_pb_converter.go",
         "log.go",
         "tempdir.go",
+        "wait_timeout.go",
     ],
     importpath = "github.com/prysmaticlabs/prysm/shared/testutil",
     visibility = ["//visibility:public"],

shared/testutil/wait_timeout.go

@@ -0,0 +1,22 @@
+package testutil
+
+import (
+	"sync"
+	"time"
+)
+
+// WaitTimeout will wait for a WaitGroup to resolve within a timeout interval.
+// Returns true if the waitgroup exceeded the timeout.
+func WaitTimeout(wg *sync.WaitGroup, timeout time.Duration) bool {
+	ch := make(chan struct{})
+	go func() {
+		defer close(ch)
+		wg.Wait()
+	}()
+	select {
+	case <-ch:
+		return false
+	case <-time.After(timeout):
+		return true
+	}
+}