feat: add strategy for file rollover

[pekasen]

Single JSONL-files per users are not really feaible for downstream database-persistance (since, we would have read the entire file and let SQLAlchemy's ORM-system figure out which things to persist).

Possible solutions:

• keep user files in a seperate directory (e.g. `.ponyuexpress' ) and after a rollover period, move their contents into a single file for each rollover period.
• do rollover in place (one file per user and rolloverperiod).