Kore rpc server should retain accumulated caches between calls

[ana-pantilie]

@jberthold pointed this out.

Impacts global caches. Examples:

• simplifier cache
• unifier cache

See also https://runtimeverification.slack.com/archives/CC360GUTG/p1665604885642499

Jost is saying this is a large issue because the server needs to be made stateful and needs better concurrency.

[ana-pantilie]

@jberthold :

• explicitly make the server single threaded
• refactor server to keep a global state
• run experiments to see if it has a positive impact on the foundry tests

To be done after KEVM is updated (in master) to use the RPC server.

[jberthold]

Some thoughts wrt. proxy server calling booster and kore-rpc:

• Each of the internal requests to execute or simplify during a proxy execute request builds up its own simplifier cache at the moment because caches are not retained between requests
• OTOH we sometimes see servers getting a very large memory footprint even without the cache persistence