[Chronik] Add support for BURN txs in slp::parse

Summary:
This has previously been unimplemented, and this diff adds support for all SLP BURN txs.

All SLP token types are parsed identically.

See here for the spec.

Test Plan: cargo test -p bitcoinsuite --test test_slp_parse_burn

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D15020