implement bandersnatch library with unit tests (#1)

• init bandersnatch

• impl Fr and Element

• add HunterGate to CMakeLists.txt

• stash import boost

• add vcpkg config

• import bandersnatch test fixture

• Fr unit tests

• modify Element, Fr and add unit tests

• remove utility/

• add github workflows

• test native workflow

• add workflows & fix bandersnatch test error