fix(api-gateway): cache GraphQL schemas per security context using visibilityMaskHash

[igorlukanin]

Check List

• Tests have been run in packages where changes have been made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Description of Changes Made (if issue reference is not provided)

GraphQL schema was cached globally, but different users have different field permissions (RBAC).

First user's schema got cached → all subsequent users saw that same schema with wrong fields.

Fix: Cache schemas per visibilityMaskHash - each unique permission set gets its own cached schema.

[codecov]

Codecov Report

❌ Patch coverage is 30.43478% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.78%. Comparing base (23b66de) to head (7d39e77).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/cubejs-api-gateway/src/gateway.ts	0.00%	8 Missing ⚠️
...ackages/cubejs-server-core/src/core/CompilerApi.ts	46.66%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10570      +/-   ##
==========================================
- Coverage   57.79%   57.78%   -0.02%     
==========================================
  Files         224      224              
  Lines       17547    17557      +10     
  Branches     3609     3613       +4     
==========================================
+ Hits        10142    10145       +3     
- Misses       6861     6867       +6     
- Partials      544      545       +1     

Flag	Coverage Δ
cube-backend	57.78% <30.43%> (-0.02%)	⬇️

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