various busy status

teracli拿到的busy状态是tabletnode定期收集的，取决于Level0的文件数；
sdk写操作拿到的busy有2个原因：一是Level0的文件数到达阈值；二是buffer满了。

这2点不一致：在buffer满时sdk得到busy，而teracli却看不到busy.

Start by tracing busy-status handling in teracli, tabletnode, and SDK write operations, focusing on Level0 file thresholds and buffer-full conditions. Reproduce the discrepancy and determine the intended shared behavior; the issue is done when teracli and SDK report busy consistently for both causes.

Written by the indexing model from the issue text.