[RFC] Lazy adapters implementation

[Koc]

Use case: some databases/search engines aren't required execute two queries for getting count and slice. So we can use only one query for slice and count, but now it doesn't work properly, because Pagerfanta filters current page so early, before slice query executed.

For preventing +1 query I've created LazyAdapterInterface that marks adapter as lazy.

TODO:

• [ ] documentation
• [x] tests

[Koc]

Example of lazy adapter for Sphinxsearch engine https://github.com/Koc/Sphinxy/blob/master/Pagerfanta/Adapter/SphinxyQbAdapter.php

[mablae]

Looks interesting for elasticsearch, too:

For example: I need aggregations from PagerfantaAdpter which are the same on all pages.

EDIT: Your PR is missing the actual LazyAdapterInterface ?

[Koc]

@mablae LazyAdapterInterface is present, but it is empty. It is just mark adapter as lazy.

[Koc]

Tests have been added

[sauron918]

Unfortunately the problem with double queries is still relevant.