[Fusion] Extend federation-gateway-audit satisfiability tests

[glen-84]

Summary

• Extend the federation-gateway-audit-derived section of SatisfiabilityValidatorTests with 15 suites across the @override, @provides, @requires, entity-call, and schema-shape clusters: 13 pass, 2 are committed as [Fact(Skip = …)].
• Lookups follow one rule: an explicit @lookup is added for every type with a resolvable @key in the audit subgraph, since the composite-schemas spec has no implicit reference resolution (Federation's implicit _entities resolver becomes an explicit @lookup).
• SDLs are adapted to the composite-schemas spec: @requires(fields:) becomes argument-level @require(field:) (including path<ConcreteType>.field type conditions), and @override(from:) uses the helper's uppercase schema names.
• The 2 skipped suites are valid supergraphs in the audit project that hit current validator gaps (circular @require, parent entity calls). Each quotes its blocker and asserts the intended IsSuccess, so it re-activates once the gap closes.
• The union-intersection suite is intentionally not ported: it would require widening an object type to a union containing it at merge time, which is out of scope.

Test plan

• dotnet test src/HotChocolate/Fusion/test/Fusion.Composition.Tests --filter "FullyQualifiedName~SatisfiabilityValidatorTests" — 61 passed, 2 skipped, 0 failed on net8.0, net9.0, and net10.0.

[Copilot]

Pull request overview

This PR extends SatisfiabilityValidatorTests with additional satisfiability suites derived from the federation-gateway-audit project, covering more directive/shape scenarios (e.g., @override, @provides, @require, entity-call, schema-shape). It also adapts the suite SDLs to the composite-schemas spec by making reference resolution explicit via @lookup and translating @requires(fields:) patterns into argument-level @require(field:).

Changes:

• Added multiple new satisfiability test cases for audit-derived scenarios, including pass and intentionally-skipped suites for known engine gaps.
• Introduced explicit @lookup @inaccessible entry points for resolvable @key types to match composite-schemas behavior.
• Updated SDLs in the new suites to composite-schemas equivalents (notably argument-level @require(field:) and updated @override(from:) schema names).

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