[v25.3.x] Fix case where messages can be written multiple times in Iceberg#29397

piyushredpanda merged 3 commits intoredpanda-data:v25.3.xredpanda-data/redpanda:v25.3.xfrom

vbotbuildovich:backport-pr-29251-v25.3.x-685vbotbuildovich/redpanda:backport-pr-29251-v25.3.x-685Copy head branch name to clipboard