query executor in constructor

[Paul-Ilyin]

PR merge checklist:

• [ ] add tests for new functionality if any

• [ ] run poetry install && pre-commit run -a

• [ ] describe changes in CHANGELOG.md with PR/issue reference like so

  ## Unreleased
  
  ### Changed
  
  - `repka.repositories.base.AsyncQueryExecutor.fetch_all` - now returns AsyncIterator (#54 by @Paul-Ilyin)
  - `repka.repositories.base.AsyncQueryExecutor.insert_many` - now returns AsyncIterator (#54 by @Paul-Ilyin)
  

• [ ] ensure build passed

Надо подумать над названием, пока ниче кроме Repository не придумал