Cardano Updates

Add basic counter test.
Add property that check for leaks in shared state.

No semantic changes: avoid `>=>`, or use `<$>` instead of `>>=`.

Add the conter thread to the test cases.
Add meta tests for AppV2 generators/shrinkers

Break out mempoolGetSnapshot into its own atomic transaction.

drop support for x86_64-darwin

connection-manager: added a comment in includeInboundConnectionImpl

This patch ensures that when a node starts syncing from scratch
in bootstrap peers mode that it has only up to 2 active connections
to bootstrap relays.

Reduce STM contention in V2 TxSubmission inbound by splitting per-peer
in-flight bookkeeping out of SharedTxState into a small per-peer
PeerTxInFlight TVar. SharedTxState is now only written when the shared
state updates. The common case of a new peer advertising an existing
txid is just a read operation for the shared state and a write operation
into the peer local TVar.

- Rename getBlockHash to getImmutableBlockPoint.
- The callback in getImmutableBlockPoint now has a dedicated GetImmutableBlockPointError error type.

tx-submission v2: return results in submitTxToMempool

Use IntSet for faster lookups for retained keys.
IntPSQ is still needed for quick removal of expeired entries.

Avoid Double conversions, similar to muxs diffTimeToMicroseconds.

Convert the direct server benchmark into one that can run multiple peers
with async.