feat: assets_state module with total supply storage

[whankinsiv]

This PR adds an assets_state module to track native asset data, currently limited to total supply per asset.

Main changes:

• Add tx.mints() processing in tx_unpacker with a new AssetDeltasMessage publisher.
• Add assets_state module, subscribing to cardano.asset.deltas to maintain total supply from mints and burns.
• Add REST handler for listing assets at /assets in rest_blockfrost.

A follow-up PR will extend assets_state with optional metadata, detailed info, and burn/mint history.

[sandtreader]

Looks great!