Fix Valgrind uninitialized memory warning when running tests

[staticssleever668]

Conditional jump or move depends on uninitialised value(s)

[Ghabry]

Jenkins: Test this please <3

[Ghabry]

Thx. Honestly not sure why its considered uninitialized but the errors are gone :)

[Ghabry]

Forwarded this change to Gemini to evaluate it: This appears to be a false positive in valgrind though I will continue merging it as it has no disadvantages.

---

Notable (I will fix this somewhere else) is that it also found a bug in flip_all:

While analyzing this file, I noticed an unrelated but highly likely bug in flip_all():
code
p[i] ^= p[i]; // <--- BUG
Any value XORed by itself is zero. Currently, flip_all() acts identically to reset_all() > (it clears all bits to 0 instead of inverting them).
To actually flip the bits, this should be written as p[i] = ~p[i]; or p[i] ^= 0xFF;.

Though this was never noticed as this function is never used and there is no unit test for it :)

[staticssleever668]

I don't think it's a false-positive, but it doesn't matter in practice either.
Memory is byte addressable. Even if we only assign and read the first n bits, we still fetch the whole byte that contains other, uninitialized bits.