Proto: Scoru: make message inbox carbonated

Context

Fixes: #2413 (closed)

Manually testing the MR

• Checked that benchmark for Sc_rollup_inbox.add_messages executes correctly

./tezos-snoop benchmark Sc_rollup_inbox_add_message and save to sc_rollup_inbox_add_message.workload --bench-num 500 --nsamples 3000 --seed 12897

Model N_IOpt_map_alpha already registered for code generation! (overloaded instruction?) Ignoring.
Model N_KIter_alpha already registered for code generation! (overloaded instruction?) Ignoring.
Model N_KList_enter_body_alpha already registered for code generation! (overloaded instruction?) Ignoring.
Model N_KMap_enter_body_alpha already registered for code generation! (overloaded instruction?) Ignoring.
Benchmarking with the following options:
{ options = { flush_cache=false;
              stabilize_gc=false;
              seed=12897;
              bench #=500;
              nsamples/bench=3000;
              determinizer=percentile 50;
              cpu_affinity=none;
              minor_heap_size=262144 words;
              config directory=None };
   save_file = sc_rollup_inbox_add_message.workload;
   storage = Mem }
Using default configuration for benchmark Sc_rollup_inbox_add_message
{ "max_bytes": 65536 }
benchmarking 500/500
stats over all benchmarks: { max_time = 228375.000000 ; min_time = 750.000000 ; mean_time = 113979.058000 ; sigma = 63738.936832 }

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR