Make `pipeline.NextRound` atomic

## Problem

The pipeline's **NextRound** is updated at the end of every round but accessed in several contexts that could be running in go-routines. A workaround we use ` atomic.LoadUint64` but that is no longer considered a best practice.

## Solution

Consider using [pipeline.NextRound.Load()](https://pkg.go.dev/sync/atomic#Uint64.Load) and similar functions for updating the variable.

### Caveat Emptor
This exact approach may not be backwards compatible on some 32-bit systems: https://go101.org/article/memory-layout.html

## Dependencies

Should wait until #128 is merged

## Urgency

Low