why hexadecimal literals are strictly signed int by default

[mrgaturus]

While creating GL bindings using glad i get some compile errors with two 
constants of type `uint64` that has 0xFFFFFFFFFFFFFFFF, it says `type mismatch: 
got <int literal(-1)> but expected 'uint64`, the problem was fixed putting 
`'u64` at the end but i wonder how this is strictly a signed int, as far i 
known hexadecimal numbers are mostly used in unsigned scenarios