Fix conv.r4/r8 conversion and type hint in ConvHandler

[wondercrash]

Sometimes conv.r4/conv.r8 would produce garbage values because the handler didn't actually convert them. Also, HandleUnknownFloatConversion was using an Integer type hint for floats instead of the Float type hint.

Example:

using System;
using System.Linq;
using AsmResolver.DotNet;
using Echo.Platforms.AsmResolver.Emulation;

var module = ModuleDefinition.FromModule(typeof(ConvTest).Module);
var type = module.TopLevelTypes.First(t => t.Name == nameof(ConvTest));

var vm = new CilVirtualMachine(module, false);
var thread = vm.CreateThread();

var convToFloat = type.Methods.First(m => m.Name == nameof(ConvTest.IntToFloat));
var r4 = thread.Call(convToFloat, [42]);
Console.WriteLine($"IntToFloat(42) = {r4!.AsSpan().F32} expected: 42");

var convToDouble = type.Methods.First(m => m.Name == nameof(ConvTest.IntToDouble));
var r8 = thread.Call(convToDouble, [-1]);
Console.WriteLine($"IntToDouble(-1) = {r8!.AsSpan().F64} expected: -1");

public class ConvTest
{
    public static float IntToFloat(int x) => (float)x;
    public static double IntToDouble(int x) => (double)x;
}

outputs:

IntToFloat(42) = 5.9E-44 expected: 42
IntToDouble(-1) = NaN expected: -1

The double cast in the Write call is necessary because otherwise it would implicitly convert it to a float. I kept the float cast for readability.

I also added a lot of tests for conv which I believe are correct.

[Washi1337]

Thanks!