remove Reverse extension to avoid source-breaking change with .NET 10

[mus65]

The internal array Reverse extension is already a little weird because it can be ambigious with Linq's Reverse(IEnumerable<T>), but behaves differently. It changes the passed array instance instead of creating a new one and returns an array instead of an IEnumerable<T>.

.NET 10 introduces a Enumerable.Reverse<T>(T[]) which causes even more ambiguity and returns an IEnumerable<T> instead of an array, which causes some compilation errors with .NET 10:

SSH.NET/test/Renci.SshNet.Benchmarks/Common/ExtensionsBenchmarks.cs(24,26): error CS0121: The call is ambiguous between the following methods or properties: 'System.Linq.Enumerable.Reverse<TSource>(TSource[])' and 'Renci.SshNet.Common.Extensions.Reverse<T>(T[])'
SSH.NET/test/Renci.SshNet.Tests/Classes/ForwardedPortDynamicTest_Stop_PortStarted_ChannelBound.cs(211,81): error CS0121: The call is ambiguous between the following methods or properties: 'System.Linq.Enumerable.Reverse<TSource>(TSource[])' and 'Renci.SshNet.Common.Extensions.Reverse<T>(T[])'
SSH.NET/test/Renci.SshNet.Tests/Classes/ForwardedPortDynamicTest_Dispose_PortStarted_ChannelBound.cs(224,81): error CS0121: The call is ambiguous between the following methods or properties: 'System.Linq.Enumerable.Reverse<TSource>(TSource[])' and 'Renci.SshNet.Common.Extensions.Reverse<T>(T[])'
SSH.NET/test/Renci.SshNet.Tests/Classes/ForwardedPortDynamicTest_SessionErrorOccurred_ChannelBound.cs(231,81): error CS0121: The call is ambiguous between the following methods or properties: 'System.Linq.Enumerable.Reverse<TSource>(TSource[])' and 'Renci.SshNet.Common.Extensions.Reverse<T>(T[])'

Looking at the usage, the Reverseextension is only needed in the context of BigInteger which already has extension methods to deal with endianness (but which were not used everywhere). So I think it makes most sense to just remove the Reverse extension.

Also introduced a ToBigInteger(this ReadOnlySpan<byte> data) which is made use of in EcdsaKey.cs.