64-bit ARM support

[lemire]

We might need to use .NET 9.0 (which is freely available in preview form).

On an Apple M2 (ARM), we are about 50% faster than the accelerated .NET functions. And twice as fast as the UTF-8 function.

After merging this PR, one needs to install https://dotnet.microsoft.com/en-us/download/dotnet/9.0

|                                       Method |                    FileName |        Mean |       Error |    StdDev | Speed (GB/s) |
|--------------------------------------------- |---------------------------- |------------:|------------:|----------:|------------- |
|                      ARMDecodingRealDataUTF8 | data/dns/swedenzonebase.txt | 11,346.6 us |   100.66 us |  26.14 us |         3.09 |
|             ARMDecodingRealDataWithAllocUTF8 | data/dns/swedenzonebase.txt | 16,834.0 us |   314.17 us |  48.62 us |         2.09 |
|                     ARMDecodingRealDataUTF16 | data/dns/swedenzonebase.txt | 15,668.2 us |   164.77 us |  25.50 us |         2.24 |
|                      ARMDecodingRealDataUTF8 |                 data/email/ |    320.9 us |     5.28 us |   1.37 us |         6.16 |
|             ARMDecodingRealDataWithAllocUTF8 |                 data/email/ |    399.5 us |    11.16 us |   1.73 us |         4.95 |
|                     ARMDecodingRealDataUTF16 |                 data/email/ |    360.1 us |    13.51 us |   3.51 us |         5.49 |
|          DotnetRuntimeSIMDBase64RealDataUTF8 | data/dns/swedenzonebase.txt | 14,892.6 us |   314.74 us |  81.74 us |         2.36 |
| DotnetRuntimeSIMDBase64RealDataWithAllocUTF8 | data/dns/swedenzonebase.txt | 17,210.5 us | 1,207.52 us | 186.87 us |         2.04 |
|             DotnetRuntimeBase64RealDataUTF16 | data/dns/swedenzonebase.txt | 31,863.2 us |   564.07 us | 146.49 us |         1.10 |
|          DotnetRuntimeSIMDBase64RealDataUTF8 |                 data/email/ |    512.1 us |     3.73 us |   0.97 us |         3.86 |
| DotnetRuntimeSIMDBase64RealDataWithAllocUTF8 |                 data/email/ |    585.1 us |     4.34 us |   0.67 us |         3.38 |
|             DotnetRuntimeBase64RealDataUTF16 |                 data/email/ |  1,797.4 us |   382.35 us |  99.30 us |         1.10 |

[lemire]

@Nick-Nuon This can be merged at will. The results are good.

[lemire]

There is a minor issue, it seems, with UTF-16... investigating.

[lemire]

@Nick-Nuon Ok. It should be good now. I have also added some new namespaces and a new file (Base64.cs), please have a look.

[Nick-Nuon]

@Nick-Nuon Ok. It should be good now. I have also added some new namespaces and a new file (Base64.cs), please have a look.

OK cool. Taking a look at it right now.

[lemire]

OK cool. Taking a look at it right now.

Splitting things up should make it easier to extend to AVX2 and AVX-512 without getting confused. :-)

[lemire]

@Nick-Nuon I think that the project is in really good shape. Lots of tests and good benchmarks. It was 'easy' for me to add ARM support. The only tricky part was the need to switch to .NET9.

[Nick-Nuon]

OK cool. Taking a look at it right now.

Splitting things up should make it easier to extend to AVX2 and AVX-512 without getting confused. :-)

It should help a bit yes :D

[Nick-Nuon]

OK it looks good, there was one minor comment that was redundant but I took the liberty to trim it.

Merging