Pointers with different residues modulo their least common allocation alignment are never equal.
Pointers to the same static allocation are equal if and only if they have the same offset.
Strictly in-bounds (in-bounds and not one-past-the-end) pointers to different static allocations are always unequal.
A pointer cannot be equal to an integer if `ptr-int` cannot be null.
Also adds more tests for `ptr_guaranteed_cmp`.
Co-authored-by: Ralf Jung <post@ralfj.de>
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