Make stacktraces more informative

[droserasprout]

Context: We often have bug reports from DipDup users containing log tail and it is not possible to get any additional information for troubleshooting.

Proposal: In order to get the most out of the log, it is proposed to improve stacktrace formatting and to enrich it with additional stack data:

• leave only frames related to the DipDup execution (skip system calls)
• Make the representation more compact (single line per frame, omit unnecessary info, leave only minimum necessary information for debugging)
• add locals, allow to filter out sensitive info (optional, bonus feature)
• improve formatting of DipDup models (implement repr, also bonus feature)

How you can test/showcase:

• force database issue by shutting down the pg instance
• implement a trivial demo indexer that raises an exception in the handler
• same, but do some illegal db actions, e.g. altering non-existing item, break constraints
• any other issues you can think of

Follow-up discussion:

• how to troubleshoot external crash reports
• what should an ideal crash report include so that one can figure out the cause of an outage and reproduce
• which existing tooling can be used to improve this process