how to access global shared variables in async handler

## code

### handle
```nim
var lock = newAsyncLock()
var fighters = @[
  Fighter(id: $genOid(), name: "隆", skill: @["波动拳"], createdAt: now().utc),
  Fighter(id: $genOid(), name: "肯", skill: @["升龙拳"], createdAt: now().utc)
]

proc listFighters(ctx: Context) {.async.} =
  await lock.acquire()
  try:
    resp jsonResponse(ok(fighters).toJson)
  finally:
    lock.release()
```
 
### routing
```nim
var fighterApi = app.newGroup("/fighter", @[])
fighterApi.get("", listFighters)
```

## error msg:

```
Expression: get(fighterApi, "", listFighters)
  [1] fighterApi: Group
  [2] "": string
  [3] listFighters: proc (ctx: Context): Future[system.void]

Expected one of (first mismatch at [position]):
[1] func get(env: Env; key: string): string
[1] proc get(app: Prologue; route: string; handler: HandlerAsync; name = "";
         middlewares: openArray[HandlerAsync] = @[])
[1] proc get[T](aq: AsyncQueue[T]): Future[T]
[1] proc get[T](self: Option[T]): lent T
[1] proc get[T](self: Option[T]; otherwise: T): T
[1] proc get[T](self: var Option[T]): var T
[3] proc get(group: Group; route: string; handler: HandlerAsync; name = "";
         middlewares: openArray[HandlerAsync] = @[])

nimble.nim(229)          buildFromDir
```