Investigate where most time is spent during syncing

[kderme]

The result of this ticket would be a report of how much time is spent in the different parts of db-sync. These include:

• applying ledger rules
• ledger snapshots
• extracting data from ledger types to Generic types.
• preparing queries and Persistent values.
• db queries and insertions. Ideally the report would be detailed, ie how much time each query takes.
• db transaction commits

[profd2004]

Closing this as part of a triage pass over the older open issues — it was already flagged stale/completed by maintainers.

The where-does-sync-time-go investigation has effectively been answered and superseded by the Persistent→Hasql rewrite in 13.7.x and the ongoing pipelining work (#2075).

Happy to reopen if there's a remaining angle worth pursuing.