Update mithril flake input from hotfix branch

## Problem The `mithril` flake input is pinned to commit `5d5571ef3421` on branch `hotfix/2543.1`. This is a hotfix branch that may not reflect the latest stable release. ## Steps 1. Check if there's a newer stable mithril release or tag 2. Update to latest stable: `nix flake update mithril` or pin to a release tag 3. Build and test