Switch to Evaera's 'roblox-lua-promise'

This could be a complete nightmare, but would be a great help in making these libraries more user friendly. The upcoming v4 release fixes all of the weird quirks, so it should be ready enough to use...

A lot of the fixes are smallish syntax things, i.e.

-- Quenty promises
function HumanoidTracker:PromiseNextHumanoid()
	if self.Humanoid.Value then
		return Promise.resolved(self.Humanoid.Value)
	end

	if self._maid._nextHumanoidPromise then
		return self._maid._nextHumanoidPromise
	end

	local promise = Promise.new()

	local conn = self.Humanoid.Changed:Connect(function(newValue)
		if newValue then
			promise:Resolve(newValue)
		end
	end)

	promise:Finally(function()
		conn:Disconnect()
	end)

	self._maid._nextHumanoidPromise = promise

	return promise
end

-- Evaera promises
function HumanoidTracker:PromiseNextHumanoid()
	if self.Humanoid.Value then
		return Promise.resolve(self.Humanoid.Value)
	end

	if self._maid._nextHumanoidPromise then
		return self._maid._nextHumanoidPromise
	end

	local promise = Promise.fromEvent(self.Humanoid.Changed, function(val)
		return val ~= nil
	end)

	self._maid._nextHumanoidPromise = promise

	return promise
end

Would also need to add a special case for the maid accepting promises, as these don't implement a .destroy method. I've been slowly converting libraries as I use them, would PRs be accepted on some separate branch?

Start by inventorying Promise usages and Maid cleanup handling across the repository, using the issue's HumanoidTracker example as a syntax reference. Compare current calls with Evaera's roblox-lua-promise v4 API, then define the migration scope and verify that promise cleanup remains supported before converting libraries.