Fix subscription initialization retries for transient WAL reads - #18829

Description

A transient NoSuchFileException during the initial region-progress WAL lookup was treated as a locate failure and thrown from poll, producing SUBSCRIPTION_POLL_ERROR (1904). This can interrupt consumers while a WAL filename is changing during rolling.

Carry an explicit RETRY_LATER decision for deferred reads and leave prefetch initialization dormant until a subsequent poll completes the lookup. Recovery frontiers and the replay cursor are installed only after a successful lookup. Confirmed retained WAL corruption remains a lookup failure, including scans that also encounter a temporarily unreadable live file.

The regression tests reproduce a file disappearing between directory listing and opening, repeated unreadable polls followed by recovery, retained corruption, and corruption followed by a deferred live-file read. Recovery checks verify that committed records are skipped and the remaining records replay exactly once without WAL gap increments.

Validation

• The new tests reproduce two initialization exceptions before the fix; all four pass with the fix.
• Related queue, seek, initialization, and WAL iterator tests: 75 tests, 0 failures, 0 errors, 1 optional performance test skipped.
• English and Chinese full-reactor test compilation passed: mvn test-compile -DskipTests and mvn test-compile -DskipTests -P with-zh-locale.
• The original 3C3D workload has not been rerun.

This PR has:

• been self-reviewed.
• added comments explaining the retry and corruption distinction.
• added unit tests covering the new behavior.

Key changed/added classes

ConsensusPrefetchingQueue, ConsensusPrefetchingQueueInitializationTest