perf(es_extended/client): only look up the closest player when the pickup prompt is used

The pickup loop calls ESX.Game.GetClosestPlayer at the top of every iteration, but
closestDistance is only read inside the nested check that runs when the player presses
the pickup control right next to a drop. As soon as any pickup is within five metres
the loop sets Sleep to 0, so the lookup runs every frame while standing near a drop.

GetClosestPlayer builds two tables and calls GetPlayers plus GetPlayerPed,
DoesEntityExist and GetEntityCoords per player, so the cost grows with the number of
players in scope - worst exactly when the server is busy.

Measured in game on artifact 25770 with a single player standing on a dropped pickup,
reading es_extended in the resource monitor over about 20 seconds each:

  before: 0.16 - 0.18 ms, sitting around 0.17
  after:  0.13 - 0.15 ms, sitting around 0.14

The two ranges do not overlap. Idle, with no pickup within five metres, is 0.04 ms in
both cases, as expected, since the loop sleeps 1500 ms then.

One player is the smallest saving this can ever show, because GetClosestPlayer scales
with the number of players in scope. The larger saving on a populated server follows
from that per player work and was not measured, testing it would need several clients.

Behaviour is unchanged, the value is computed in the same frame it is used.

[core]/es_extended/client/modules/events.lua

@@ -372,7 +372,6 @@ if not Config.CustomInventory then
         while true do
             local Sleep = 1500
             local playerCoords = GetEntityCoords(ESX.PlayerData.ped)
-            local _, closestDistance = ESX.Game.GetClosestPlayer(playerCoords)
 
             for pickupId, pickup in pairs(pickups) do
                 local distance = #(playerCoords - pickup.coords)
@@ -383,6 +382,8 @@ if not Config.CustomInventory then
 
                     if distance < 1 then
                         if IsControlJustReleased(0, 38) then
+                            local _, closestDistance = ESX.Game.GetClosestPlayer(playerCoords)
+
                             if IsPedOnFoot(ESX.PlayerData.ped) and (closestDistance == -1 or closestDistance > 3) and not pickup.inRange then
                                 pickup.inRange = true