Replace per-session pool trimming with pressure hysteresis

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

src/stats/me_getters.rs

@@ -204,6 +204,12 @@ impl Stats {
         self.buffer_pool_in_use_gauge.load(Ordering::Relaxed)
     }
 
+    /// Returns the count of non-standard buffers replaced before pooling.
+    pub fn get_buffer_pool_replaced_nonstandard_total(&self) -> u64 {
+        self.buffer_pool_replaced_nonstandard_total
+            .load(Ordering::Relaxed)
+    }
+
     pub fn get_me_c2me_send_full_total(&self) -> u64 {
         self.me_c2me_send_full_total.load(Ordering::Relaxed)
     }

src/stats/mod.rs

@@ -274,6 +274,7 @@ pub struct Stats {
     buffer_pool_pooled_gauge: AtomicU64,
     buffer_pool_allocated_gauge: AtomicU64,
     buffer_pool_in_use_gauge: AtomicU64,
+    buffer_pool_replaced_nonstandard_total: AtomicU64,
     // C2ME enqueue observability
     me_c2me_send_full_total: AtomicU64,
     me_c2me_send_high_water_total: AtomicU64,

src/stats/writer_counters.rs

@@ -552,6 +552,14 @@ impl Stats {
         }
     }
 
+    /// Publishes the cumulative count of non-standard pool buffer replacements.
+    pub fn set_buffer_pool_replaced_nonstandard_total(&self, value: usize) {
+        if self.telemetry_me_allows_normal() {
+            self.buffer_pool_replaced_nonstandard_total
+                .store(value as u64, Ordering::Relaxed);
+        }
+    }
+
     pub fn increment_me_c2me_send_full_total(&self) {
         if self.telemetry_me_allows_normal() {
             self.me_c2me_send_full_total.fetch_add(1, Ordering::Relaxed);