Add new flag "return nothing" in options for DML operations

[wey1and]

It is necessary to add the "return nothing" flag to the options of such functions as: truncate(), replace(), etc. Where the return of a function is not so important, but performance may be required.

The same was in TDG2 https://github.com/tarantool/tdg2/issues/1450

[Totktonada]

It is especially important for crud.*_many() operations (see PR #232). I propose noreturn name.

[DifferentialOrange]

There is a question about what exactly "no value" value is. let's discuss existing API first.

Core Tarantool space:upsert does not return any values with nil response. crud.upsert success response is { rows = {}, metadata = ... }, while crud.upsert_many is { metadata = ... } (res.rows == nil) (see also #357). TDG2 skip_result returns empty array instead of array with data.

So we have the following response alternatives for (at least partially) successful noreturn operation:

• { rows = {}, metadata = ... }
• { metadata = ... }
• {}
• true
• nil

(Bear in mind that in the case of the last three alternatives, we'll need to support noreturn for upsert operations too.)

The main motivation of noreturn is to reduce the overhead on useless tuple transfer between router and storage. It seems that the solution on this side would be roughly the same for all of the alternatives. But there is the other point: to reduce the overhead on useless info transfer between the router and the connector (like go-tarantool, tarantool-python, cartridge-java). In this case, the latter -- nil -- seems better.

On the other hand, receiving nil, nil in case of success may be a little confusing. But since noreturn is an optional one and the user of noreturn will know exactly what they expect, it seems fine.

(It is also worth to mention that in case of *_many operations we may have partial success with resp, errs that will transfer to nil, errs. But since the user of noreturn does not interested in what exactly has been succeed, it should be fine.)