fix: close HttpClient after binlog download to prevent resource leak (#5579)

BinlogDownloadQueue.download() creates a CloseableHttpClient for each
download but never closes it. Over time this exhausts connection pool
resources. Wrap the HTTP execution in a try-finally block to ensure the
client is always closed.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>