Integrate Piece Directory into booster-bitswap

[dirkmc]

booster-bitswap needs to make two calls to the underlying blockstore implementation:

• GetSize to get the size of the block (and check if the blockstore has the block)
• Get to get the block data

At the moment these calls go from booster-bitswap to boostd to the sealing subsystem.

We should update booster-bitswap to

• Call the Piece Directory to get the block's size and offset (using the Piece Directory Client)
• Fetch the block data directly from the sealing subsystem (instead of going through boostd)