[Chronik] Add MempoolTokens to index mempool token txs
Summary:
Parses, colors, validates and indexes mempool txs as SLP/ALP txs.
In fetch_tx_spent_tokens, bulk-query ops are used wherever possible. It is exposed so we can use it in the indexer later, too.
Test Plan: cargo test -p chronik-db test_mempool_tokens
Reviewers: Fabien, #bitcoin_abc
Reviewed By: Fabien, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D15099