Replace the internal sha512 implementation with .Net built in sha512

[niklasfp]

This pr replaces the internal implementation of Sha512 to use the Sha512 in the .Net framwork.

It also removes the files that were there only to support the internal Sha512 implementation.

The benefits are:

• Simplification by removing code not needed to be maintained
• Easier path to e.g. remove allocations in Nkey because of the methods that supports spans etc.
• Less allocations
• Speed

Removed methods

This pr also removes some methods from the Sha512 internal wrapper class, they were all unused internal methods.

public void Update(ArraySegment<byte> data)
public void Finalize(ArraySegment<byte> output)
public static byte[] Hash(byte[] data)

Micro benchmarks

BenchmarkDotNet v0.13.12, macOS Sonoma 14.3.1 (23D60) [Darwin 23.3.0]
Apple M2 Pro, 1 CPU, 12 logical and 12 physical cores
.NET SDK 8.0.101
  [Host]   : .NET 8.0.1 (8.0.123.58001), Arm64 RyuJIT AdvSIMD
  ShortRun : .NET 8.0.1 (8.0.123.58001), Arm64 RyuJIT AdvSIMD

Job=ShortRun  IterationCount=3  LaunchCount=1  
WarmupCount=3  

Main
| Method     | Iter | Mean     | Error   | StdDev  | Gen0     | Allocated |
|----------- |----- |---------:|--------:|--------:|---------:|----------:|
| NKeyCreate | 5000 | 142.9 ms | 5.23 ms | 0.29 ms | 500.0000 |   4.08 MB |

This pr
| Method     | Iter | Mean     | Error   | StdDev  | Gen0     | Allocated |
|----------- |----- |---------:|--------:|--------:|---------:|----------:|
| NKeyCreate | 5000 | 142.8 ms | 2.23 ms | 0.12 ms | 250.0000 |    2.9 MB |
 
Main 
| Method     | Iter | DataSize | Mean      | Error    | StdDev   | Gen0     | Allocated |
|----------- |----- |--------- |----------:|---------:|---------:|---------:|----------:|
| Sha512Hash | 5000 | 1024     |  17.95 ms | 0.346 ms | 0.019 ms | 187.5000 |    1.6 MB |
| Sha512Hash | 5000 | 25600    | 396.04 ms | 4.489 ms | 0.246 ms |        - |    1.6 MB |

This pr
| Method     | Iter | DataSize | Mean      | Error     | StdDev    | Gen0    | Allocated |
|----------- |----- |--------- |----------:|----------:|----------:|--------:|----------:|
| Sha512Hash | 5000 | 1024     |  4.991 ms | 0.3914 ms | 0.0215 ms | 46.8750 | 429.69 KB |
| Sha512Hash | 5000 | 25600    | 84.237 ms | 1.3626 ms | 0.0747 ms |       - | 429.81 KB |

[niklasfp]

@mtmk is this a flapper: https://github.com/nats-io/nats.net.v2/actions/runs/7855013069/job/21436316896?pr=390#step:7:302

It's the Slow_consumer test, and seems to work fine locally.

[mtmk]

@mtmk is this a flapper: https://github.com/nats-io/nats.net.v2/actions/runs/7855013069/job/21436316896?pr=390#step:7:302

It's the Slow_consumer test, and seems to work fine locally.

yes. we have #344 to take care of them soon.

[mtmk]

is this disposable?

[niklasfp]

is this disposable?

Yes it is, doh!! I'll add disposable on the wrapper and make sure we dispose it where appropriate
Sorry about that, should have caught this myself.

[niklasfp]

@mtmk Added IDisposable and usings where needed.

[mtmk]

LGTM thanks @niklasfp 💯

[caleblloyd]

LGTM