Cardano Updates

Enrich db-immutaliser to print info about the candidates in a
VolatileDB. This is useful when analyzing a VolatileDB with a priori
unknown content (especially when it contains various forks).

Concretely, it will print all maximal candidates, as well as a block
tree illustrating the fork relation.

An invocation looks like this (also see the updated README section):
```
db-immutaliser --immutable-db /path/to/immutable --volatile-db /path/to/volatile --config /path/to/config.json \
  --verbose --dot-out /path/to/block-tree.dot --dry-run
```

Here, `/path/to/out-imm` must be the path to an appropriate ImmutableDB
(we are only processing volatile blocks that are reachable from the
immutable tip) that will *not* be modified here due to `--dry-run` (new
in this PR). In the simple case where no blocks are immutable yet (which
can be the case for short-lived testnets), this can just be an empty
directory.

The resulting block tree can be visually rendered as a graph, see the
README, or
https://github.com/IntersectMBO/ouroboros-consensus/pull/1482#issuecomment-2828083404
for an example.

---

A potential alternative is to put this into a separate tool, but that
could also happen later.

Payloads and connecting peers forced me ot figure out how to not always persist
chains all the way back to Origin. Which forced me to realize and handle some
weird corner cases.

I'm optimistic, but I do expect friction once this is finally connected to the
actual tests.