oracledb_cdc: switch from buffering records to streaming

[josephwoodward]

This change switches from buffering LogMiner results to streaming them, reducing memory allocations.

Before is left, after is right:

[claude]

Commits
LGTM

Review
Clean refactor that switches queryLogMinerContents from buffering all redo events into a slice to streaming them via a callback — good for memory efficiency on large SCN ranges.

1. Error context loss for processing failures — processRedoEvent errors now bubble up through queryLogMinerContents without wrapping and get attributed to "querying logminer contents" at the call site, losing the previous "process redo event" context. Comment

[claude]

Commits
LGTM

Review
Clean refactoring of queryLogMinerContents from buffering all redo events into a slice to streaming them through a callback. The change eliminates intermediate memory allocation while preserving identical behavior. Error wrapping, context propagation, deferred rows.Close(), CSF fragment handling, and rows.Err() checking are all correct.

LGTM