- [x] Improve subscription API to detect when the client drops and stop listening
- [ ] Improve the detection of drop-client reactive, instead of waiting until an attempted delivery fails.
- [ ] Implement the filter by status
- [ ] Implement the filter by since / until (this is implemented at the primary key level at the cursor)
- [ ] Have more tests
- [ ] Move the broadcasting of events to a different thread
- [ ] Stop the working thread when the ledger goes out of scope

Bonus

- [ ] Improve the HashMap of Filter to use the filter much more efficiently with the primary key (similar to the cursor)