Clay Monger, alongside Bursts of Rain implementation

This PR adds the new enemy on the roadmap, the Clay Monger, concepted by Rekka, Modelled and Animated by DotFlare and programmed by yours truly.

This is a VERY SIZEABLE change to the project, some of the key changes to point out:

The Chirristmas event now lasts during the entire week where the 25th of december falls. this is constant across all years, so this year it'll be from the 23rd of December to the 29th of December
This change has been done to mimick the new event comming for another special month we've discussed.
Due to the new event also including a pickup-abble enemy, the component that gave players a chirristmas hat has been changed so it can work in a relatively gfeneric way, it's been renamed to "SpecialEventPickup"
MSU has been updated to the latest indev version.

More importantly, due to the intensive scripting related to the Clay Monger's Tar Trail, some new things have been added to the project itself.

SS2 now depends on Bursts of Rain, this package gives us access to the following packages ingame that allow for high performance with the Clay Monger:
- Burst
- Collections
- Collections itself has a dependency on mono.cecil by default which causes issues, the bulletpoint below mathematics addresses this by adding a new import extension that handles this kind of issue.
- Mathematics
The project itself now utilizes the RoR2 Thunder Burster unity package, this package allows us to easily burstify our assembly utilizing our existing pipeline setups, due to changes related to the import process, it is EXTREMELY recommended to reimport the game.
The MongerTarTrailManager class handles the implementation of numerous C# jobs that are burst compiled, this should be used alongside the regular tar trail for managing puppies. However, the non bursted version is still present in the project, this should not be used and its there purely as a backup.

TeamMoonstorm / Starstorm2