[Chronik] Optimize prepare_indexed_txs by using batch queries and removing redundancy

Summary:
Currently, prepare_indexed_txs is doubly inefficient:

1. If two inputs spend two outputs from the same tx, it'll query the tx num of this tx twice
2. It queries tx nums one-by-one, instead of utilizing the optimized batch query gets that RocksDB provides

We fix this by adding batch query versions to LookupColumn and TxReader, and then utilize those in prepare_indexed_txs.

Note: We can't use sorted_inputs anywhere in this function when querying input_tx_nums, since those can come in a random order.

Benchmarks show there's a speedup of about 1.6 when syncing the first 300000ish blocks:

Test Plan: ninja check-crates && ninja check-functional

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15571