`is_producer` assumptions

[TanyaS08]

So for both the adbm as well as l matrix function one of the parameters we need to make a decision on is 'status' of a species as a producer...

So there are two ways I can see us doing this. One we make it a trait and treat it as an expert knowledge opinion and thus guarantee that producers have an out degree of zero. Alternatively we remove the producer clause from both functions and use the assumption that the bodymass ratio will take care of all of those issus...

[TanyaS08]

Update 1 -> not needed for ADBM but still an l-matrix assumption

Update 2 -> in terms of needing it for the l-matrix. my interpretation is that it is related to just splitting out species from a ratio perspective (we expect $x$ proportion of spp to be basal). Which theoretically means we could exclude it as a term and just let the bodyside component be the determinant