* Fixes pooled timer leaking
* Fixes `[dumptimers` command so it outputs properly, adds spacing, and stacktraces
* Adds `[Tidy]` for serializing Lists. This will remove deleted entities during world save before serializing the list.
* Adds helpers for managing Lists/Sets/Dictionaries
### New API
```cs
// Creates the list if it is null, then adds
Utility.Add(ref list, value);
Utility.Add(ref set, value);
Utility.Add(ref dict, key, value);
// Nulls the variable if the count is zero
Utility.Remove(ref list, value);
Utility.Remove(ref set, value);
Utility.Remove(ref dict, key);
// Marks entity as dirty in addition to doing the action
entity.Add(list, value);
// Marks entity as dirty, and will create list if it doesn't exist
entity.Add(ref list, value);
// Marks entity as dirty in addition to doing the action
entity.Remove(list, value);
// Marks entity as dirty, and will null the list count is zero
entity.Remove(ref list, value);
```
### Updates to [dumptimers
<img width="825" alt="Screen Shot 2021-08-14 at 2 55 10 AM" src="https://user-images.githubusercontent.com/3953314/129442449-ccf7fe14-29d6-4f3f-9366-c8eb7b9828a7.png">
* Optimizes OrderedHashSet using the learnings here: https://github.com/dotnet/runtime/issues/10050
* Removes ValueCollection since it was a relic from the conversion of the OrderedDictionary
* Centralizes throw strings.
* Adds pooled ordered hash set (but doesn't use it)
Closes#448
