[EIP-4399 2/3] Added total difficulty stage and transition logic (#2964)

* added diff stage

* added td stage

* improvements + more tests

* added err check

* added err check

* transition raw interfaces

* interface for transition

* unwind updates

* maybe this fix

* now fixed?

* fixes

* better db-format

* better db-format

* sum and mod

* sum and mod

* fixed headers unwind