refactor(streamingRequest): internal method for request functions

- TS package type inference for request functions.
- Type fix for Lua's waitFor callback.
- Lua request functions cannot return nil.

imports/streamingRequest/client.lua

@@ -0,0 +1,19 @@
+---@async
+---@package
+---@generic T : string | number
+---@param request function
+---@param hasLoaded function
+---@param assetType string
+---@param asset T
+---@param timeout? number
+---@param ... any
+---Used internally.
+function lib.streamingRequest(request, hasLoaded, assetType, asset, timeout, ...)
+    if hasLoaded(asset) then return asset end
+
+    request(asset, ...)
+
+    return lib.waitFor(function()
+        if hasLoaded(asset) then return asset end
+    end, ("failed to load %s '%s'"):format(assetType), timeout)
+end