Minor Optimizations and Bugfixes

Yes, I tested it. It compiles and runs without errors, and same warnings as before.

Added player movement by forces into FixedUpdate to make it framerate independent.

Did some more optimization by commenting out unused Update functions (they still run when empty), storing components in variables, removing non-necessary allocation, and replacing comparison operator for tags with CompareTag function.

Moved camera into late update so it updates after player updates their position so it follows correctly.

Fixed null reference exception that occurs when firing grow gun at nothing. There is another that occurs when firing the grow gun on the bullets of enemies, because the bullets do not have a maximum or minimum size. I didn't fix that one because I don't know how you want it handled.