[fix] [ml] fix discontinuous ledger deletion (#20898)
### Motivation
- The task `trim ledgers` runs in the thread `BkMainThreadPool.choose(ledgerName)`
- The task `write entries to BK` runs in the thread `BkMainThreadPool.choose(ledgerId)`
So the two tasks above may run concurrently/
The task `trim ledgers` work as the flow below:
- find the ledgers which are no longer to read, the result is `{Ledgers before the slowest read}`.
- check if the `{Ledgers before the slowest read}` is out of retention policy, the result is `{Ledgers to be deleted}`.
- if the create time of the ledger is lower than the earliest retention time, mark it should be deleted
- if after deleting this ledger, the rest ledgers are still larger than the retention size, mark it should be deleted
- delete the`{Ledgers to be deleted}`
**(Highlight)** There is a scenario that causes the task `trim ledgers` did discontinuous ledger deletion, resulting consume messages discontinuous:
- context:
- ledgers: `[{id=1, size=100}, {id=2,size=100}]`
- retention size: 150
- no cursor there
- Check `ledger 1`, skip by retention check `(200 - 100) < 150`
- One in-flight writing is finished, the `calculateTotalSizeWrited()` would return `300` now.
- Check `ledger 2`, retention check `(300 - 100) > 150`, mark the ledger-2 should be deleted.
- Delete the `ledger 2`.
- Create a new consumer. It will receive messages from `[ledger-1, ledegr-3]`, but the `ledger-2` will be skipped.
### Modifications
Once the retention constraint has been met, break the loop.
