Parallel notifications, correct ordering for switch statement cases

[martinothamar]

Solves #115 and #138

• INotificationPublisher abstraction similar to that of MediatR, apart from making the interface slightly worse while allowing better performance (avoiding closures, same as for the pipeline behavior interface)
• Ordering of requests when building the compilation model now makes switch statements correct when there is inheritance and the base classes aren't abstract

TODO

• Better naming?

Benchmarks

BenchmarkDotNet v0.13.12, Pop!_OS 22.04 LTS
AMD Ryzen 5 5600X, 1 CPU, 12 logical and 6 physical cores
.NET SDK 8.0.201
  [Host]     : .NET 8.0.2 (8.0.224.6711), X64 RyuJIT AVX2
  DefaultJob : .NET 8.0.2 (8.0.224.6711), X64 RyuJIT AVX2

Method	ServiceLifetime	Mean	Error	StdDev	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
SendNotification_Baseline	Singleton	0.0145 ns	0.0073 ns	0.0068 ns	1.00	0.00	1	-	-	NA
SendNotification_Mediator	Singleton	11.1046 ns	0.0460 ns	0.0408 ns	1,016.06	668.32	2	-	-	NA
SendNotification_IMediator	Singleton	20.3442 ns	0.0262 ns	0.0232 ns	1,860.85	1,223.14	3	-	-	NA
SendNotification_MessagePipe	Singleton	31.7092 ns	0.0606 ns	0.0538 ns	2,902.13	1,909.50	4	0.0005	40 B	NA
SendNotification_MediatR	Singleton	100.1991 ns	0.2711 ns	0.2117 ns	8,401.17	5,794.82	5	0.0033	288 B	NA