Bury coefficients should be in their own datatype, not particulate_share

[mnlevy1981]

The *_share_type variables are to store data that needs to be passed from the base tracer module to the carbon isotopes but isn't already in memory (e.g. instead of passing zooplankton_local, we sum some elements over the zooplankton_cnt dimension). By this definition, the bury coefficients should not be in particulate_share.

Where they should be is a harder question. Perhaps in their own bury_coeff_type? Or maybe they fit into an existing type.

[mnlevy1981]

This may be easily addressed alongside either #53 or #324