[BUG] [Go] Json Unmarshal int bigger then int64

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

in the go generator, trying to unMarshal big int values, get overflow on int64

package main

import (
	"encoding/json"
	"fmt"

	"github.com/danijeel/bigintexample/openapi"
)

func main() {
	jsonSrc := []byte(`{
		"id": 162259276829213363391578010288126,
		"name": "test"
	}`)
	var myJson openapi.Category
	json.Unmarshal(jsonSrc, &myJson)
	fmt.Printf("%d\n", myJson.Id)
	// output: 824634459072
	// expects: 162259276829213363391578010288126
}

Full example can be seen here: https://github.com/danijeel/bigintexample/blob/main/main.go

openapi-generator version

5.2.1

OpenAPI declaration file content or url

The openapi example specification is based on the petstore example
https://github.com/danijeel/bigintexample/blob/eb590428c496e152ec32ff30a6464b2849b74a7b/openapi.yml

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

In the branch patch-big-int
I replaced the int64 attribute with custom type BigInt in the category model

https://github.com/danijeel/bigintexample/commit/97dde59dd7b6ec4aa136431de31268dda248bb74

Start by reproducing the overflow with the linked openapi.yml and the Go example in main.go, then inspect the generated openapi.Category model and its Id field. Compare the generated int64 field with the custom BigInt change in the linked patch-big-int branch. Done should mean the generated Go model preserves the large JSON integer instead of producing the shown overflow.