Mock ledger formatting and CI/CD check hook

[jmagan]

This pull request focuses on code cleanup, formatting improvements, and dependency adjustments in the mock-ledger/backend subproject, as well as some workflow updates.

[SpaceManiac]

Looks like a straightforward improvement 👍. Long term I think we want the root workspace to also include the mock ledger instead of the CI script having to mention it separately, but it doesn't have to be in this PR.

---

LFDT policy wants a Signed-off-by line on commits to indicate acknowledgement of the developer certificate of origin. The full info is in the failing check, but the easy way to fix this is:

1. To fix this PR, run git rebase main --signoff then force-push
2. For future commits, use git commit -s, or create a script .git/hooks/commit-msg with something like the following to automatically do it:

   #!/bin/sh
   git interpret-trailers --if-exists doNothing --trailer "Signed-off-by: $(git config user.name) <$(git config user.email)>" --in-place "$1"