feat : support for conv3D forward

Context

issue : #38 (closed), aidge#252 (closed)

Added :

• Conv3D
• ConvTranspose3D
• Pad3D
• PaddedConv3D
• PaddedConvTranspose3D

Enhancements

Conv1D & Conv2D backward functions have been optimized : indexing is now done by only incrementing the index counters without using multiplication.

Before

for (DimSize_t kX = 0; kX < kDim[0]; ++kX) {
    kOffsets[2] = kX * kStrides[2] + kOffsets[1];
    iDilKernelOffsets[0] = kX * dilation[0] * iStrides[2];

    // DOING STUFF ...........
}

After

iDilKernelOffsets[0] = 0;
kOffsets[2] = kOffsets[1];
for (DimSize_t kX = 0; kX < kDims[0]; ++kX,
               kOffsets[2] += kStrides[2],
               iDilKernelOffsets[0] += dilation[0] *
                                       iStrides[2]) {
    // DOING STUFF ...........
}

NOTE : This implies a bit of unconventionnal over-crowding the for loops. That is usually written as :

for (DimSize_t kX = 0; kX < kDims[0]; ++kX) {
    // DOING STUFF ...........
    kOffsets[2] += kStrides[2];
    iDilKernelOffsets[0] += dilation[0] * iStrides[2];
}

but since the the //DOING STUFF....... usually contains 3+ nested loops, this would quickly be un-readable. Hence I chose to use the 1st "overcrowded for loop" syntax.