[v24.2.x] archival: bump offset if seeking undershoots

[vbotbuildovich]

Backport #23937 to branch v24.2.x. This issue was created as a placeholder because the original PR's commit(s) could not be automatically cherry-picked.
Here are the commands to execute:

git checkout v24.2.x
git checkout -b manual-backport-23937-v24.2.x-746
git cherry-pick -x 8b616df65b ff120d0d74 5e99303170 5f18ba97c5

git push origin manual-backport-23937-v24.2.x-746
gh pr create \
  --title "[v24.2.x] `archival`: bump offset if seeking undershoots" \
  --base "v24.2.x" \
  --label "kind/backport" \
  --head "manual-backport-23937-v24.2.x-746" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v24.2.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/23937 "