Disable perf sampling on iter next (MystenLabs#11007)

## Description 

Iter `next` is called way more than seek. Sampling on seek is ok but on
next even though we are only incrementing an atomic counter, the sample
function consumes a lot of cpu.

## Test Plan 

Existing tests

crates/typed-store/src/rocks/iter.rs

@@ -1,12 +1,10 @@
 // Copyright (c) Mysten Labs, Inc.
 // SPDX-License-Identifier: Apache-2.0
-use std::{marker::PhantomData, sync::Arc};
+use std::marker::PhantomData;
 
 use bincode::Options;
 use rocksdb::Direction;
 
-use crate::metrics::{DBMetrics, SamplingInterval};
-
 use super::{be_fix_int_ser, errors::TypedStoreError, RocksDBRawIter};
 use serde::{de::DeserializeOwned, Serialize};
 
@@ -15,26 +13,15 @@ pub struct Iter<'a, K, V> {
     db_iter: RocksDBRawIter<'a>,
     _phantom: PhantomData<(K, V)>,
     direction: Direction,
-    cf: String,
-    db_metrics: Arc<DBMetrics>,
-    iter_bytes_sample_interval: SamplingInterval,
     is_initialized: bool,
 }
 
 impl<'a, K: DeserializeOwned, V: DeserializeOwned> Iter<'a, K, V> {
-    pub(super) fn new(
-        db_iter: RocksDBRawIter<'a>,
-        cf: String,
-        db_metrics: &Arc<DBMetrics>,
-        iter_bytes_sample_interval: &SamplingInterval,
-    ) -> Self {
+    pub(super) fn new(db_iter: RocksDBRawIter<'a>) -> Self {
         Self {
             db_iter,
             _phantom: PhantomData,
             direction: Direction::Forward,
-            cf,
-            db_metrics: db_metrics.clone(),
-            iter_bytes_sample_interval: iter_bytes_sample_interval.clone(),
             is_initialized: false,
         }
     }
@@ -64,19 +51,10 @@ impl<'a, K: DeserializeOwned, V: DeserializeOwned> Iterator for Iter<'a, K, V> {
                 .expect("Valid iterator failed to get value");
             let key = config.deserialize(raw_key).ok();
             let value = bcs::from_bytes(raw_value).ok();
-            if self.iter_bytes_sample_interval.sample() {
-                let total_bytes_read = (raw_key.len() + raw_value.len()) as f64;
-                self.db_metrics
-                    .op_metrics
-                    .rocksdb_iter_bytes
-                    .with_label_values(&[&self.cf])
-                    .observe(total_bytes_read);
-            }
             match self.direction {
                 Direction::Forward => self.db_iter.next(),
                 Direction::Reverse => self.db_iter.prev(),
             }
-
             key.and_then(|k| value.map(|v| (k, v)))
         } else {
             None

crates/typed-store/src/rocks/mod.rs

@@ -1337,12 +1337,7 @@ impl<'a> DBTransaction<'a> {
         let db_iter = self
             .transaction
             .raw_iterator_cf_opt(&db.cf(), db.opts.readopts());
-        Iter::new(
-            RocksDBRawIter::OptimisticTransaction(db_iter),
-            db.cf.clone(),
-            &db.db_metrics,
-            &db.iter_bytes_sample_interval,
-        )
+        Iter::new(RocksDBRawIter::OptimisticTransaction(db_iter))
     }
 
     pub fn keys<K: DeserializeOwned, V: DeserializeOwned>(
@@ -1640,12 +1635,7 @@ where
                 .read_perf_ctx_metrics
                 .report_metrics(&self.cf);
         }
-        Iter::new(
-            db_iter,
-            self.cf.clone(),
-            &self.db_metrics,
-            &self.iter_bytes_sample_interval,
-        )
+        Iter::new(db_iter)
     }
 
     fn safe_iter(&'a self) -> Self::SafeIterator {
@@ -1712,12 +1702,7 @@ where
                 .read_perf_ctx_metrics
                 .report_metrics(&self.cf);
         }
-        Iter::new(
-            db_iter,
-            self.cf.clone(),
-            &self.db_metrics,
-            &self.iter_bytes_sample_interval,
-        )
+        Iter::new(db_iter)
     }
 
     fn keys(&'a self) -> Self::Keys {