Improve perfomance json decoding using go-json

[n9te9]

Description

See related:

• Proposal for Custom JSON Encoder/Decoder #2757
• Improve: optimize graphql runtime #3372
• [Proposal] Allow passing a custom json marshal/unmarshal implementation #2842
• replace encoding/json with goccy/go-json (#2421 expanded) #3161

This PR optimizes JSON decoding. Specifically:
These changes aim to improve the performance of the gqlgen server, especially in high-throughput scenarios.

Related Issue
Resolves #3372 (replace with actual issue link)

Benchmark

I took benchmark simple code.
schema is generated project initialization.

resolver implementation

// CreateTodo is the resolver for the createTodo field.
func (r *mutationResolver) CreateTodo(ctx context.Context, input model.NewTodo) (*model.Todo, error) {
	return &model.Todo{}, nil
}

// Todos is the resolver for the todos field.
func (r *queryResolver) Todos(ctx context.Context) ([]*model.Todo, error) {
	return []*model.Todo{}, nil
}

// Messages is the resolver for the messages field.
func (r *subscriptionResolver) Messages(ctx context.Context) (<-chan *model.Message, error) {
	return make(chan *model.Message), nil
}

// Mutation returns MutationResolver implementation.
func (r *Resolver) Mutation() MutationResolver { return &mutationResolver{r} }

// Query returns QueryResolver implementation.
func (r *Resolver) Query() QueryResolver { return &queryResolver{r} }

// Subscription returns SubscriptionResolver implementation.
func (r *Resolver) Subscription() SubscriptionResolver { return &subscriptionResolver{r} }

go test bench overview is below.

# encoding/json
$ go test -bench . -benchmem -cpuprofile=cpu.prof -memprofile=mem.prof
goos: darwin
goarch: amd64
pkg: github.com/99designs/gqlgen/cmd/benchmark_tests
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkPost-16       	    3578	    316744 ns/op	   21447 B/op	     155 allocs/op
BenchmarkGet-16        	    2896	    383965 ns/op	   21101 B/op	     161 allocs/op
BenchmarkWebsock-16    	    2947	    397610 ns/op	   20414 B/op	     159 allocs/op

# goccy/go-json
$ go test -bench . -benchmem -cpuprofile=cpu-improve.prof -memprofile=mem-improve.prof
goos: darwin
goarch: amd64
pkg: github.com/99designs/gqlgen/cmd/benchmark_tests
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkPost-16       	    4328	    262948 ns/op	   20910 B/op	     155 allocs/op
BenchmarkGet-16        	    3211	    354725 ns/op	   20547 B/op	     157 allocs/op
BenchmarkWebsock-16    	    3070	    368349 ns/op	   20286 B/op	     156 allocs/op

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)