Defer disconnecting connections in signal:Destroy() to reflect native RBXScriptSignal behavior + Trove type improvements

[PolarisStarSystem]

modules/signal/init.luau

• Defer disconnecting connections in signal:Destroy(), so that any calls to signal:FireDeferred(...) during the same resumption cycle but before the signal:Destroy() call will fire to the connections.

• _proxyHandler disconnection is deferred with the rest of the connections.

• This reflects native Roblox behavior when calling rbxScriptSignal:Fire(...) and then destroying a parent Instance, which still fires to its connections even with workspace.SignalBehavior set to Deferred.

• These changes bring back old behavior as outlined in Cancel waiting threads if signal disconnects all connections #164 (comment), but only when signal:Destroy() is used instead. signal:DisconnectAll() retains its current behavior.

• Move signal:DisconnectAll() behavior to new function called disconnectSignalConnectionsStartingFromItem and removed references to _handlerListHead in the new function. _handlerListHead is cleared immediately and sent to the new function from both signal:DisconnectAll() and signal:Destroy() instead.

• connection:Disconnect() is unchanged as calling rbxScriptSignal:Fire(...) and then rbxScriptConnection:Disconnect() does not fire to the rbxScriptConnection when using Deferred SignalBehavior.

• connection:Destroy() is unchanged as there is no equivalent to it in RBXScriptConnection.

• Changed some comments and function documentation which may need to be rewritten and new ones may need to be added. Documentation for signal:Destroy() should be updated at the very least.

modules/signal/init.test.luau

• Added 3 new tests

• Added new function called DeferCondition to replace AwaitCondition where signal:FireDeferred(...) is used for better test accuracy in theory.

• Tests were not ran in the other modules so it's possible behavior could be different, although unlikely.

[PolarisStarSystem]

I added some type improvements to Trove to this pull request. I would make a new pull request for this, but I do not see a simple way of doing that, so this will do.

Improvements are as follows:

• Add missing Once function type to the Trove export type.

• Only return ConnectionLike with Connect and Once in the Trove export type so the script editor properly lints the returned connection. This one I'm not 100% on because you'll get a type error if you pass the returned connection to a function that has a connection type argument with a metatable or is a RBXScriptConnection. Might be better to just deal with it add a unioned RBXScriptConnection to the return type instead.

• Add [any]: any to Trackable types. This fixes the union type checking error when you do something like this:

local cleanup = Trove.new()
local signal = Signal.new()
cleanup:Connect(signal)

• Add unioned RBXScriptConnection return type to Connect and Once in SignalLike and SignalLikeMetatable. This fixes the union type checking error when you type cast a TypedRemote and connect it like this:

local cleanup = Trove.new()
local event = TypedRemote.event("foo") :: TypedRemote.Event<>
cleanup:Connect(event.OnServerEvent, function() end)

The union type errors are issues I ran into related to the native Roblox type checker.