Poh subsystem cleanup, genesis plumbing, enable real PoH on edge testnet (#4292)

* Remove unused PohServiceConfig::Step

* Clarify variable name

* Poh::hash() now takes an iteration counter

* man -> max

* Inline functions with single call site

* Move PohServiceConfig into GenesisBlock

* Add plumbing to enable real PoH on testnets

* Batch hashes to improve PoH hash rate

* Ensure a constant hashes_per_tick

* Remove PohEntry mixin field

* Poh/PohEntry no longer maintains tick_height

* Ensure a constant hashes_per_tick

* ci/localnet-sanity.sh: Use real PoH

* Rework Poh/PohService to keep PohRecorder unlocked as much as possible while hashing

sdk/src/poh_config.rs

@@ -0,0 +1,29 @@
+use crate::timing::DEFAULT_NUM_TICKS_PER_SECOND;
+use std::time::Duration;
+
+#[derive(Serialize, Deserialize, Clone, Debug)]
+pub struct PohConfig {
+    /// The target tick rate of the cluster.
+    pub target_tick_duration: Duration,
+
+    /// How many hashes to roll before emitting the next tick entry.
+    /// None enables "Low power mode", which implies:
+    /// * sleep for `target_tick_duration` instead of hashing
+    /// * the number of hashes per tick will be variable
+    pub hashes_per_tick: Option<u64>,
+}
+
+impl PohConfig {
+    pub fn new_sleep(target_tick_duration: Duration) -> Self {
+        Self {
+            target_tick_duration,
+            hashes_per_tick: None,
+        }
+    }
+}
+
+impl Default for PohConfig {
+    fn default() -> Self {
+        Self::new_sleep(Duration::from_millis(1000 / DEFAULT_NUM_TICKS_PER_SECOND))
+    }
+}