[feature]: decimal display support pt. 2

[jharveyb]

Addressing #925 , continuation of #930 .

• [x] Only encode non-default (non-zero) precision values.
• [x] Reject mints if the existing JSON metadata is too big to add the precision field to, if precision was specified.
• [x] On reissuance, fetch the precision from the asset metadata (if possible) of the asset group anchor, and assert equality with the reissuance request. -- "Precision should be fixed for all issuances in an asset group"
• [x] display new precision field on some (?) RPC responses -- ListAssets, ListTransfers, and the address-related RPC calls