fix: retry standby imports while PALF recovers

[wangyunlai-seekdb]

Backport

Backport of #1360 to release/1.4.0.

Problem

After a primary-to-standby switchover, restarting the former primary can start standby log sync while PALF is still in RECOVERING. The import path returned OB_STATE_NOT_MATCH (-4109), which the standby sync service recorded as fatal even though PALF becomes ACTIVE shortly afterwards.

Fix

Return OB_EAGAIN only for the transient PALF RECOVERING state. The periodic sync task retries it; other non-append states and all log-continuity failures remain OB_STATE_NOT_MATCH.

Validation

• git diff --check
• The equivalent change built successfully on the master PR (fix: retry standby imports while PALF recovers #1360).
• Release-branch build initialization is currently blocked before compilation because its dependency manifest requests obshell-4.5.0.1-52026082614.al8.x86_64.rpm, which the configured mirror returns as HTTP 404.