There were some weird constants I stripped out from the Asset model

[uberbrady]

We have a chunk of weird constants and methods that we really didn't need to have in the Asset model. This PR pulls those out and just looks directly at assigned_type and compares to things like User::class et al.

I think this is easier to read and understand, and the additional abstractions were just confusing.

Tests pass, but that doesn't mean much. I'm happy to take a more deep pass through the code if we decide that this is even a direction we like.

Oh, and there were some code improvements I made to the assetLoc method that I think make it a bit cleaner to read.

[what-the-diff]

PR Summary

• Optimization in Asset Handling: Code that was redundant or not in use, like the portion handling check if an asset is assigned to a user in AssetCheckinController.php, has been removed. This results in a neater code structure and less clutter.

• Improved Clarity in AccessoryCheckout.php: Better comment notation has been added to improve overall code readability and maintenance for future developers.

• Enhanced Recursion Control: A new constant, MAX_ASSET_ITERATIONS_FOR_LOCATION, has been introduced in Asset.php. This will be used to limit the depth of checking asset locations, adding an additional layer of protection against unwanted infinite loops.

• Logic Refactoring: Decision-making processes in Asset.php have been refined and superfluous methods are removed, making our code leaner, easier to understand, and more efficient.

• Improved Location Checking: The manner in which asset locations are checked has been refined in assetLoc method in Asset.php, resulting in more efficient and clearer code.

• Updated Testing Procedures: Tests in StoreAssetTest.php have been altered such that they now check the assigned type directly instead of indirectly. This change paves the way for more straightforward and error-proof testing of code. The clearer test cases will facilitate pinpointing and rectifying problems faster.