fix: tarantool yields on load metadata while holding mut reference

Previously for every query we hold a mutable reference on an engine and tried to load a cluster metadata if the cache was empty. The problem was that tarantool yields on a first query uploading the cache to a new one, that also tries to get a mutable reference to the engine. The main problem was that we should never hold a mutable reference to an object with a Lua code, that can be yielded by tarantool (such behavior is opaque to the Rust compiler). To deal with it we shrink a metadata upload to a list of separate methods. For the ones that can yield we always hold an immutable reference. Those methods that need a mutable reference to the engine never yield.