BatchScanRegions should check context

[lhy1024]

Enhancement Task

Now, BatchScanRegions ignores ctx and holds RegionTree read lock, which will block heartbeats if it hold lock for long periods.

Under heavy batch-scan traffic, requests can run for 10+ minutes, keeping the read lock and starving writes (CheckAndPutRootTree uses r.t.Lock()). This blocks region heartbeat updates.

[2026/01/01 00:22:46.092 +08:00] [WARN] [interceptor.go:197] ["request stats"] ["start time"=2026/01/01 00:11:09.834 +08:00] ["time spent"=11m36.258304292s]

BatchScanRegions should stop scanning on cancellation/deadline and we should reduce log

[okJiang]

@lhy1024 Which version is the screen?

In my impression, the lock optimization of BatchScanRegion should have been implemented in master

[lhy1024]

@lhy1024 Which version is the screen?

In my impression, the lock optimization of BatchScanRegion should have been implemented in master

8.5.3

[okJiang]

In my impression, the lock optimization of BatchScanRegion should have been implemented in master

It had been reverted 😂 #9674