Revisit forward sync constants

[tbenr]

DEFAULT_FORWARD_SYNC_BATCH_SIZE = 50
considering that this number has been set pre-merge when beacon blocks were small and state transition was fast, maybe we should lower this down to 25. moreover we now have blobs, so the batch implies a 50*6 (that will be 8 or 9 for ELECTRA) blobs in the batch.

DEFAULT_FORWARD_SYNC_MAX_BLOCKS_PER_MINUTE = 500
this is even more important because it implies a blob limit 500*6 (that will be 8 or 9 for ELECTRA), which are a lot of objects per minute, which might be the reason why we got rate limited in the NFT devnet.
I think the best approach would be to add a specific PER_MINUTE constant for blobs. So we don't need to lower down the block value too much. The rational is to avoid impacting sync performance when syncing outside the data availability window (18gg), where we don't try do download blobs at all.