fix(graphql-limit-count): measure each fragment once when computing query depth

[shreemaan-abhishek]

Description

graphql-limit-count computes a query's selection-nesting depth (used as the rate-limit cost) by expanding fragment spreads in place. The cycle guard (visited) was cleared after each descent, so a fragment referenced from more than one place was fully re-measured on every occurrence. When fragments reference other fragments repeatedly, the depth computation grows exponentially in the number of fragments, so a small document can become expensive to process in the access phase.

This memoizes each fragment's resolved depth so a fragment is measured once regardless of how many times it is spread. visited still guards fragment cycles; a new memo table caches the per-fragment result, keeping the traversal linear in the document size. The computed depth is unchanged for existing queries.

Added tests: a route whose query reuses fragments many times now returns normally instead of stalling the worker.

Which issue(s) this PR fixes:

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible

[membphis]

[P2] Fragment memoization caches a cycle-context-dependent depth

memo is keyed only by fragment name, but the cached depth also depends on the current visited recursion stack. With mutually recursive fragments, the first traversal can cache an incomplete depth and reuse it from another path, making the computed cost traversal-order-dependent and potentially undercounting quota usage.

Please avoid memoizing cycle-dependent results, for example by excluding cyclic fragment components from memoization or rejecting cyclic fragment graphs, and add regression tests for mutually recursive fragments reached at different nesting depths and in different traversal orders.