[v25.2.x] Split read recovery memory equally between partitions

[vbotbuildovich]

Backport #27428 to branch v25.2.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 v25.2.x
git checkout -b manual-backport-27428-v25.2.x-65
git cherry-pick -x 780710f4ef aceb27d66d 6a1d9a98e6

git push origin manual-backport-27428-v25.2.x-65
gh pr create \
  --title "[v25.2.x] Split read recovery memory equally between partitions" \
  --base "v25.2.x" \
  --label "kind/backport" \
  --head "manual-backport-27428-v25.2.x-65" \
  --draft \
  --repo "redpanda-data/redpanda" \
  --milestone "v25.2.x-next" \
  --body "Backport of PR https://github.com/redpanda-data/redpanda/pull/27428 "