#23 issues in src/tests_core.cpp when building/running with UBSan

[Oliver Lee]

When building rng_test with UBSan, I am seeing UB due to invalid shifts and out of bounds access.

src/tests_core.cpp:3060:23: runtime error: shift exponent 32 is too large for 32-bit type 'int'
src/tests_core.cpp:3299:11: runtime error: index -2 out of bounds for type 'Uint32[256]' (aka 'unsigned int[256]')
src/tests_core.cpp:3310:20: runtime error: index -1 out of bounds for type 'Uint32[256]' (aka 'unsigned int[256]')
src/tests_core.cpp:1861:48: runtime error: index 1024 out of bounds for type 'Uint8[1024]' (aka 'unsigned char[1024]')
src/tests_core.cpp:2782:22: runtime error: index 256 out of bounds for type 'Uint32[256]' (aka 'unsigned int[256]')