Add functional-methods to make it easier to transform blocks & models.

[marcromeyn]

Goals ⚽

This PR adds methods like map, filter, walk to our blocks. This makes it easier to transform models. This would enable things like adapters, something like:

def llora(module):
    if isintance(module, (nn.Linear, nn.Embedding)):
        return LoRALayer(module)
​
    return module
​
with_adapters = Block(....).walk(llora)

[github-actions]

Documentation preview

https://nvidia-merlin.github.io/models/review/pr-1194