[chronik-client] Update GenesisInfo to return hex string for data key of ALP tokens

Summary:
This matches existing patterns in chronik-client. IMO we should stick to hex strings for API returns. API returns for tokens -- esp GenesisInfo -- needs to be cached as it never changes. Caching Uint8Array is complicated because it is not JSON. But hex strings are easy.

ecash-lib has available toHex and fromHex methods that make conversion easy depending on dev needs.

auth as a Uint8Array would require special handling in Cashtab's existing caching mechanism if we do not make this change.

Test Plan: CI tests

Reviewers: #bitcoin_abc, tobias_ruck

Reviewed By: #bitcoin_abc, tobias_ruck

Subscribers: tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D17194