Get_contracts: add measurement of contracts' mem consumption.

Context

This change modifies get_contracts script so that it additionally outputs a *.size file for each analysed script, containing the memory footprint of the contract in the script cache. This is computed by parsing each contract's code into Script_ir_translator.ex_code and calling Obj.reachable_words on it. This let's us easily track memory footprint of individual contracts, but more importantly, to get an overall view of how memory footprint of smart contracts changes from one protocol to the next.

Manually testing the MR

$ dune exec devtools/get_contracts/get_contracts_012_Psithaca.exe /path/to/the/context /path/to/output

Observe the *.size file generated for each script.

Checklist

• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR