Leaky breeki

Fun fact: I don't dogfood this. My personal server ended up having to be more stable than I originally wanted (due to it being run autonomously), and my testbench isn't really capable of battle-testing this stuff.

Changed

• Custom-wrote certain string-handling functions for a significant speedup on long strings, especially on Windows. pl_barnblitz on a Windows server had a 250x speed gain in entity parsing, while writing had a 270x speed gain (bringing both operations down to below frametime at 1/66th of a second)

Fixed

• Handles just being removed from the list and not actually freed on LevelEntityList.Erase()
• Cloned handles not being properly moved to plugins calling LevelEntityList.Get(), at which point attempting to delete the handle would quietly fail