Add more benchmarks

[pekkah]

Add new benchmarks for additional scenarios and performance testing.

• ExecutionBenchmarks.cs

  • Add benchmark methods Query_with_large_response, Mutation_with_large_payload, and Subscription_with_high_frequency.

• AdditionalBenchmarks.cs

  • Create new benchmark class AdditionalBenchmarks.
  • Add benchmark methods ComplexQuery_with_multiple_fragments, Mutation_with_nested_inputs, and Subscription_with_large_payload.
  • Implement Setup method to initialize benchmark documents.

• PerformanceBenchmarks.cs

  • Create new benchmark class PerformanceBenchmarks.
  • Add benchmark methods Query_with_deeply_nested_fields, Mutation_with_large_array, and Subscription_with_high_throughput.
  • Implement Setup method to initialize benchmark documents.

• GraphQL.Benchmarks.csproj

  • Add AdditionalBenchmarks.cs and PerformanceBenchmarks.cs to the project.

• README.md

  • Update instructions to include running new benchmarks.

• Utils.cs

  • Add utility methods InitializeLargeQuery, InitializeLargeMutation, and InitializeHighFrequencySubscription.

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