• Rename RequireRecvCtx to TryReceive
• Rename RequireSendCtx to RequireSend
• Remove unused AssertSendCtx
• Add RequireReceive function that will fail the test if the chan is closed

These new names more clearly describe their functionality.

• The primary purpose of these helpers doesn't actually center around contexts, and mostly uses them as a way to cancel the channel read if the test times out.
• RequireRecvCtx as it was implemented didn't actually require that you could read a value from the chan. It would just return a zero value if the chan was closed.
• The new RequireReceive properly requires that a value is received from the chan.