Calculate point based on vertex pairs

We should add the following connivence function for `calculate_p` where instead of specifying indices in an `ind_to_ind_value_map` we can assume single site ind per vertex and just pass vertices
Similar to
```julia
function calculate_p(input, s::IndsNetworkMap)
ndim = dimension(s)
x = zeros(ndim)
for (v, value) in input
ind = only(s[v])
d = dimension(s, ind)
x[d] += index_value_to_scalar(s, ind, value - 1)
end
return x
end
```

Search the implementation and existing uses of `calculate_p` and inspect how `IndsNetworkMap` maps vertices to indices. Add the convenience form that accepts vertex-value pairs and verify that it produces the same point as the index-based form, using any existing `calculate_p` tests or examples if available.

Written by the indexing model from the issue text.