Fix prefetching the same GQL type for batch request

[grynchuk]

I have issue with getting wrong prefetch data while query in batch mode. In short, first query prefetch specific data and set it to prefetch buffer, second query use previous query prefetch buffer instead of using its own and get incomplete data set. I have to note that this issue is relates to prefetching of nested data, see test for mo details.

Request:

[
  {
    "query": "query { contact (name: "Joe") { name  posts { id  title } } }",
  },
  {
    "query": "query { company (id: "1"){ name contact  { name  posts { id  title } } } }",
  }
]

Response
Actual:

[{"data":{"contact":{"name":"Joe","posts":[{"id":1,"title":"First Joe post"}]}}},{"data":{"company":{"name":"Company","contact":{"name":"Kate","posts":null}}}}]

Expected:

[{"data":{"contact":{"name":"Joe","posts":[{"id":1,"title":"First Joe post"}]}}},{"data":{"company":{"name":"Company","contact":{"name":"Kate","posts":[{"id":3,"title":"First Kate post"}]}}}}]

[oojacoboo]

Thanks for the PR @grynchuk! Everything looks pretty good - some CS fixes needed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.29%. Comparing base (53f9d49) to head (5364cde).
Report is 68 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #658      +/-   ##
============================================
- Coverage     95.72%   95.29%   -0.44%     
- Complexity     1773     1818      +45     
============================================
  Files           154      171      +17     
  Lines          4586     4841     +255     
============================================
+ Hits           4390     4613     +223     
- Misses          196      228      +32     

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[andrew-demb]

@oojacoboo These fixes merged for the 7.x version of graphqlite, but there's a major performance problem with 7.x which is blocked update for 7.x for the Symfony bundle - thecodingmachine/graphqlite-bundle#203 (comment)
And issue in graphqlite - #691

Would you approve PR with the same changes, but for 6.x branch of graphqlite (and tag an additional 6.x release after merge)?

[oojacoboo]

@andrew-demb maybe it's just a better idea to test the changes in class-finder as per the comments in #691 and get that resolved, instead of just back patching, to prevent resolving the actual issue, assuming that you're even seeing any degraded performance.