record,tool: add a facility to print chunk-level details of a log file

It's difficult to understand a log (WAL or MANIFEST) file that's invalid or corrupt. We don't have a way to print the binary structure (eg, chunks and their headers, checksums, etc). We could restructure the code so that we expose iterators over blocks and chunks, and use that to implement a new command in `tool` that provides this context.

Jira issue: PEBBLE-394

Start by reading the record and tool code that handles WAL and MANIFEST files, then trace how blocks and chunks are currently parsed. The proposed facility would expose iterators over those structures and add a tool command that prints chunk headers, checksums, and related binary details. Done means invalid or corrupt log files can be inspected at chunk level.

Written by the indexing model from the issue text.