perf: eliminate LINQ allocations in GameplaySampleTriggerSource and ColourHitErrorMeter hot paths

Agent-Logs-Url: https://github.com/winnerspiros/osu/sessions/b0878070-74cc-41e1-af2d-af6fb8954594

Co-authored-by: winnerspiros <1675249+winnerspiros@users.noreply.github.com>

Author: Copilot

osu.Game/Rulesets/UI/GameplaySampleTriggerSource.cs

@@ -102,10 +102,25 @@ protected override void Update()
             {
                 // We need to use lifetime entries to find the next object (we can't just use `hitObjectContainer.Objects` due to pooling - it may even be empty).
                 // If required, we can make this lookup more efficient by adding support to get next-future-entry in LifetimeEntryManager.
-                var candidate =
-                    // Use alive entries first as an optimisation.
-                    hitObjectContainer.AliveEntries.Keys.Where(e => !isAlreadyHit(e)).MinBy(e => e.HitObject.StartTime)
-                    ?? hitObjectContainer.Entries.Where(e => !isAlreadyHit(e)).MinBy(e => e.HitObject.StartTime);
+
+                // Use alive entries first as an optimisation (single-pass minimum, no LINQ allocation).
+                HitObjectLifetimeEntry? candidate = null;
+
+                foreach (var e in hitObjectContainer.AliveEntries.Keys)
+                {
+                    if (!isAlreadyHit(e) && (candidate == null || e.HitObject.StartTime < candidate.HitObject.StartTime))
+                        candidate = e;
+                }
+
+                // Fall back to full entries if no alive non-judged entry found.
+                if (candidate == null)
+                {
+                    foreach (var e in hitObjectContainer.Entries)
+                    {
+                        if (!isAlreadyHit(e) && (candidate == null || e.HitObject.StartTime < candidate.HitObject.StartTime))
+                            candidate = e;
+                    }
+                }
 
                 // In the case there are no non-judged objects, the last hit object should be used instead.
                 if (candidate == null)

osu.Game/Screens/Play/HUD/HitErrorMeters/ColourHitErrorMeter.cs

@@ -115,10 +115,32 @@ public void Push(HitErrorShape shape)
 
             private void removeExtraJudgements()
             {
-                var remainingChildren = Children.Where(c => !c.IsRemoved);
+                // Count non-removed children and remove excess starting from the oldest.
+                // This avoids re-enumerating via LINQ .Count()/.First() on every iteration.
+                int remaining = 0;
 
-                while (remainingChildren.Count() > JudgementCount.Value)
-                    remainingChildren.First().Remove();
+                foreach (var c in Children)
+                {
+                    if (!c.IsRemoved)
+                        remaining++;
+                }
+
+                int target = JudgementCount.Value;
+
+                if (remaining <= target)
+                    return;
+
+                foreach (var c in Children)
+                {
+                    if (remaining <= target)
+                        break;
+
+                    if (!c.IsRemoved)
+                    {
+                        c.Remove();
+                        remaining--;
+                    }
+                }
             }
 
             private void updateMetrics()