Use atomic field updaters in selected Uni places

[jponge]

• Avoid allocating excessive amounts of AtomicReference instances
• Improve abstraction over internal state of UniOperatorProcessor
• Use further atomic field updaters in selected places (Uni)
• Use CaS methods in UniOperatorProcessor

[jponge]

@Sanne You can review this

[codecov]

Codecov Report

Merging #669 (5c7a7bc) into main (a526e97) will increase coverage by 0.12%.
The diff coverage is 86.66%.

❗ Current head 5c7a7bc differs from pull request most recent head e06ce7d. Consider uploading reports for the commit e06ce7d to get more accurate results

@@             Coverage Diff              @@
##               main     #669      +/-   ##
============================================
+ Coverage     89.85%   89.98%   +0.12%     
- Complexity     2976     2981       +5     
============================================
  Files           374      374              
  Lines         11752    11757       +5     
  Branches       1476     1476              
============================================
+ Hits          10560    10579      +19     
+ Misses          611      604       -7     
+ Partials        581      574       -7     

Impacted Files	Coverage Δ
...ye/mutiny/operators/uni/UniOnCancellationCall.java	77.14% <77.77%> (+1.38%)	⬆️
.../smallrye/mutiny/operators/uni/UniRetryAtMost.java	77.50% <81.81%> (+1.18%)	⬆️
...allrye/mutiny/operators/uni/UniOnCancellation.java	85.18% <88.88%> (+1.18%)	⬆️
...rye/mutiny/operators/uni/UniOperatorProcessor.java	80.76% <90.00%> (+3.49%)	⬆️
...mallrye/mutiny/operators/uni/UniFailOnTimeout.java	81.63% <100.00%> (ø)
...lrye/mutiny/operators/uni/UniOnFailureFlatMap.java	80.00% <100.00%> (ø)
...utiny/operators/uni/UniOnItemOrFailureFlatMap.java	87.80% <100.00%> (ø)
.../mutiny/operators/uni/UniOnItemTransformToUni.java	83.33% <100.00%> (ø)
...mallrye/mutiny/helpers/queues/MpscLinkedQueue.java	90.32% <0.00%> (-8.07%)	⬇️
.../io/smallrye/mutiny/helpers/queues/DrainUtils.java	75.55% <0.00%> (-4.45%)	⬇️
... and 14 more

[jponge]

Supersedes #660

[Sanne]

Looks good!

[Sanne]

I'll be testing it soon with the Techempower benchmark as well, but I see no reason to wait for it.