Fix Cell Hash Issues in Block BoC Formation

[inyellowbus]

Problems

• In some cases, a block's BoC could not be formed (Cell.fromBoc) — the calculated hash of exotic cells did not match the hash recorded inside the cell.
• In some cases, the rootHash of a block (rootCell.hash(0)) obtained using Cell.fromBoc did not match the rootHash obtained from tonCenter for the same block.

Solutions

• In the getRepr function, when calling getBitsDescriptor, the bits of that cell are now always used (prior to the fix, a hash could be passed in, breaking the reading)
• In serialization.ts readCell() function, added reading (reader.skip) of hashes and depths recorded inside the cell.

Block hashes are now calculated correctly

[dvlkv]

LGTM but can you provide tests?