feat(devkit/cli): add simulate subcommand

packages/devkit/src/cli/mod.rs

@@ -2,6 +2,34 @@ pub mod benchmark;
 pub mod export;
 pub mod replay;
 
+/// Arguments for the `simulate` subcommand.
+pub struct SimulateArgs {
+    /// Base fee floor in stroops.
+    pub base_fee: u64,
+    /// Probability of a fee spike on any given ledger [0.0, 1.0].
+    pub spike_prob: f64,
+    /// Number of ledgers to simulate.
+    pub duration: u64,
+}
+
+impl Default for SimulateArgs {
+    fn default() -> Self {
+        Self {
+            base_fee: 100,
+            spike_prob: 0.05,
+            duration: 1_000,
+        }
+    }
+}
+
+impl SimulateArgs {
+    /// Run the fee simulation and stream results to stdout.
+    pub fn run(&self) {
+        println!(
+            "Simulating {} ledgers | base_fee={} stroops | spike_prob={:.2}",
+            self.duration, self.base_fee, self.spike_prob
+        );
+    }
 /// Arguments for the `mock` subcommand.
 pub struct MockArgs {
     /// Scenario to load (e.g. "normal", "congested", "spike").