Cardano Updates

This patch fixes a bug where results `TVar` was never initialised if all
local root peers were provided with their IP addresses, and thus the
node didn't try to connect to any of its local root peers.

We add `LocalRootPeersResult` to `TestTraceEvent` which is used to track
values committed to the `TVar` which holds local root peers with
resolved dns names.  It is more robust to use `traceTVarIO` than to
relay on `TraceLocalRootPeers` events, as  we can force the latter to be
traced even if there's no dns name to be resolved.  This captures the
case where local root peers contains only IP addresses.

It's no longer necessary to worry about exporting the default
constructor for `TokenMap`.

The original concern was that exporting the default constructor would
allow callers to break the invariant that there are no `mempty` values
in the map.

However, this is no longer possible, as the `MonoidMap` type handles
this invariant automatically.

Therefore, it's no longer necessary to have a warning.

Nevertheless, this commit doesn't export the default constructor, as
there currently isn't any need to do so.

The `TokenMap` type has an invariant that:
- no `mempty` values appear within the internal data structure.
- no `mempty` values appear within any encoding of a `TokenMap`.

The `MonoidMap` type already guarantees to handle this invariant, and that
type is covered by a comprehensive test suite.

Therefore, there's no need to repeat those tests for the `TokenMap`
type.

This patch fixes a bug where results `TVar` was never initialised if all
local root peers were provided with their IP addresses, and thus the
node didn't try to connect to any of its local root peers.

We add `LocalRootPeersResult` to `TestTraceEvent` which is used to track
values committed to the `TVar` which holds local root peers with
resolved dns names.  It is more robust to use `traceTVarIO` than to
relay on `TraceLocalRootPeers` events, as  we can force the latter to be
traced even if there's no dns name to be resolved.  This captures the
case where local root peers contains only IP addresses.