Improve burmMem / equalMemFull performance

[arnetheduck]

• Linux and Windows define special c functions for clearing memory that the compiler is guaranteed to not remove - in addition to being safer, they are typically also faster (because they don't have to operate byte-by-byte)
• equalMemFull can be implemented using unrolling and larger limbs than byte resulting in a significant speedup - this PR also removes some of the range checking done by previous code that would introduce branching in the C code where non is desired