Fix: merge composite scopes in final selection

[gmac]

Fixes a bug with the final filtering of non-distinct composite field selections, per #87.

The Problem

Multiple selection scopes applied to the same object selection were not getting combined in the final result, for example:

query {
  shop1 {
    products {
      id
    }
    products {
      name
    }
  }
}

While this query properly fetched all requested data from underlying services (i.e.: query planning worked as expected), the resulting data only included fields for the first distinct products selection scope:

{
  "data": {
    "shop1": {
      "products": [
        {
          "id": "gid://shopapp/Product/7"
          // ack, no "name"
        }
      ]
    }
  }
}

The Fix

This adjusts unionAndTrimSelectionSetRec, where the mapping of "seenFields" was filtering all repeated selection names as though they were leaf values. This new implementation has repeat composite fields merge their selections together.

Resolves #87.

[codecov-commenter]

Codecov Report

Merging #104 (188c1c1) into main (d2cc7fd) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #104      +/-   ##
==========================================
- Coverage   67.50%   67.49%   -0.02%     
==========================================
  Files          24       24              
  Lines        2736     2738       +2     
==========================================
+ Hits         1847     1848       +1     
- Misses        739      740       +1     
  Partials      150      150              

Impacted Files	Coverage Δ
query_execution.go	69.83% <100.00%> (+0.12%)	⬆️
auth.go	86.79% <0.00%> (-0.63%)	⬇️

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[pkqk]

Good find

[lucianjon]

Wicked, thanks @gmac