Add hardening tests

[sse245]

Adds a test suite for the hardening bonus. The following things are tested and should be handled appropriately by a student's implementation:

• Missing magic constant
• Sizes of constant and text pool exceed file size

For the above tests the student's implementation should return -1 for init_ijvm.

• Invalid instructions (both normal and after WIDE)
• Underflowing the stack
• DUP, IFEQ, IFLT, ISTORE, and IRETURN on an empty stack
• IADD, IAND, IOR, ISUB, SWAP, and IF_ICMPEQ on a stack with a single element
• GOTO, IFEQ, IFLT, IF_ICMPEQ, LDC_W, IINC, and INVOKEVIRTUAL are only followed by one byte
• GOTO, IFEQ, IFLT, IF_ICMPEQ, and INVOKEVIRTUAL branching outside the text area
• LDC_W on an empty constant pool
• ILOAD, ISTORE, and WIDE do not have a successive byte
• INVOKEVIRTUAL's short is not a valid index into the constant pool
• IRETURN on the "main" method

For the above tests the student's implementation should cause a successive call to finished() to return true. The invalid code should not cause any errors like segmentation faults, but an error message can be printed.

• IADD and ISUB overflow
• IADD and ISUB underflow

For the above tests the student's implementation should match the behaviour of Java. For an overflow that means that the number rolls over from 2147483647 to -2147483648 and continues the operation from there. For an underflow that means that the number rolls over from -2147483648 to 2147483647 and continues the operation from there.

Sanitizers should be run separately and should not indicate any errors.