Bump solidity >=0.8.13

[Chomtana]

Motivation

Currently there are many files with solidity >=0.8.7

Solution

Find all and replace >=0.8.7 with >=0.8.13

I have already submit my name to contributor in #348

[Chomtana]

Forge test compiler should be updated first.

Anyway, local test is passing

[0age]

Aaah, this is intended; all of the reference contracts are built using 0.8.7 as it was recommended as a good, battle-tested version of the solidity compiler to compare against!