Upstream non-Leios commits from the Leios integration branch to master

Companion to IntersectMBO/cardano-api#1291.

**Before starting: confirm with Sebastian Nagel which Leios integration branch is the relevant one** (`leios-prototype` and `jl/leios-prototype-remake` both exist).

The Leios integration branch carries changes that are not Leios-specific and should land on master rather than diverge on the prototype branch.

Task:
- Confirm the relevant branch with Sebastian.
- Audit its commits and identify everything that builds against released dependencies — noting that some picks may depend on the corresponding cardano-api changes reaching master first.
- Bring those changes onto master via normal PRs — cherry-pick where the commits apply cleanly, or manually integrate where they don't.
- Rebase the Leios branch so it carries only Leios-specific work.