fix: circuit flamegraphs with segmentation (#1571)

The circuit flamegraphs being generated were incorrect due to a bug in
the multi-segment execution logic. In particular, each segment takes the
metric data from the previous segment, but the first segment was using
an empty metrics struct instead of being initialized with the correct
`fn_bounds` data.

Author: Avaneesh-axiom

crates/vm/src/arch/vm.rs

@@ -178,6 +178,12 @@ where
         );
         let pc = exe.pc_start;
         let mut state = VmExecutorNextSegmentState::new(memory, input, pc);
+
+        #[cfg(feature = "bench-metrics")]
+        {
+            state.metrics.fn_bounds = exe.fn_bounds.clone();
+        }
+
         let mut segment_idx = 0;
 
         loop {