This provides a lightweight alternative to ExecutableNormalizedOperation
(ENO) for tracking query complexity during validation.

New features:
- QueryComplexityLimits class with maxDepth and maxFieldsCount settings
- Configuration via GraphQLContext using QueryComplexityLimits.KEY
- Fragment fields counted at each spread site (like ENO)
- Depth tracking measures nested Field nodes
- New validation error types: MaxQueryDepthExceeded, MaxQueryFieldsExceeded

Implementation notes:
- Fragment complexity is calculated lazily during first spread traversal
- No additional AST traversal needed - complexity tracked during normal
  validation traversal
- Subsequent spreads of the same fragment add the stored complexity

Usage:
```java
QueryComplexityLimits limits = QueryComplexityLimits.newLimits()
    .maxDepth(10)
    .maxFieldsCount(100)
    .build();

ExecutionInput input = ExecutionInput.newExecutionInput()
    .query(query)
    .graphQLContext(ctx -> ctx.put(QueryComplexityLimits.KEY, limits))
    .build();
```

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Move introspection abuse detection from execution-time ENO creation to
the validation layer. This eliminates the expensive
ExecutableNormalizedOperation construction for every introspection query.

The validator now enforces two checks when GOOD_FAITH_INTROSPECTION is
enabled: field repetition (__schema/__type max once, __Type cycle fields
max once) and tightened complexity limits (500 fields, 20 depth).

Co-Authored-By: Claude Opus 4.6 <[email protected]>