concurrent map writes

debug模式下
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context/data_context.go:371 ==> Vars[variable] = newValue.
限制同时10个50个goroutinue并发请求，均出现过concurrent map writes，map读写问题。

请求场景：
func API(ctx context.Context, req *Request) error {
data := make(map[string]interface{})
data["req"] = req
data["stg_name"] = &stgName

err, _ = engine.EngPool.ExecuteSelectedRules(data, stgRule)
// do sth ...
}

release并未发现。

Start at context/data_context.go:371, where Vars[variable] = newValue is reported, and reproduce the issue in debug mode with 10–50 concurrent goroutines using the API and ExecuteSelectedRules scenario from the report. Done means the concurrent request case no longer produces a Go concurrent map writes failure; verify the release behavior as well.

Written by the indexing model from the issue text.