fix: CI errors batch 2 - missing using, nullable, pattern matching, redundant casts, unused usings

Agent-Logs-Url: https://github.com/winnerspiros/osu/sessions/45232cd1-6884-4c60-815e-dba288232c8c

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

Author: Copilot

osu.Game.Rulesets.Catch/UI/Catcher.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Buffers;
 using System.Diagnostics;
-using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;

osu.Game.Rulesets.Osu/Mods/OsuModRelax.cs

@@ -7,6 +7,7 @@
 using System.Linq;
 using osu.Framework.Localisation;
 using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Objects.Drawables;
 using osu.Game.Rulesets.Objects.Types;
 using osu.Game.Rulesets.Osu.Objects;
 using osu.Game.Rulesets.Osu.Objects.Drawables;

osu.Game.Rulesets.Osu/Objects/Drawables/DrawableOsuHitObject.cs

@@ -6,7 +6,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;

osu.Game.Rulesets.Osu/Objects/Drawables/DrawableSlider.cs

@@ -166,8 +166,8 @@ protected override void LoadSamples()
 
             // HitSampleInfo : ISampleInfo (reference type) — array covariance lets us cast directly,
             // avoiding a second array allocation from .Cast<ISampleInfo>().ToArray().
-            Samples.Samples = (ISampleInfo[])HitObject.TailSamples.ToArray();
-            slidingSample.Samples = (ISampleInfo[])HitObject.CreateSlidingSamples().ToArray();
+            Samples.Samples = HitObject.TailSamples.ToArray();
+            slidingSample.Samples = HitObject.CreateSlidingSamples().ToArray();
         }
 
         public override void StopAllSamples()

osu.Game.Rulesets.Osu/Objects/Drawables/DrawableSpinner.cs

@@ -143,7 +143,7 @@ protected override void LoadSamples()
         {
             base.LoadSamples();
 
-            spinningSample.Samples = (ISampleInfo[])HitObject.CreateSpinningSamples().ToArray();
+            spinningSample.Samples = HitObject.CreateSpinningSamples().ToArray();
             spinningSample.Frequency.Value = spinning_sample_initial_frequency;
 
             maxBonusSample.Samples = new ISampleInfo[] { new SpinnerBonusMaxSampleInfo(HitObject.CreateHitSampleInfo()) };
@@ -352,7 +352,7 @@ private void updateBonusScore()
             while (completedFullSpins.Value != spins)
             {
                 // Manual forward scan avoids allocating a LINQ delegate per spin completion.
-                DrawableSpinnerTick? tick = null;
+                DrawableSpinnerTick tick = null;
 
                 foreach (var t in ticks)
                 {

osu.Game.Rulesets.Osu/Objects/Drawables/SliderInputManager.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Input;
@@ -95,8 +94,7 @@ public void PostProcessHeadJudgement(DrawableSliderHead head)
 
             foreach (var nestedObj in slider.NestedHitObjects)
             {
-                var nested = nestedObj as DrawableOsuHitObject;
-                if (nested == null) continue;
+                if (nestedObj is not DrawableOsuHitObject nested) continue;
 
                 // Skip nested objects that are already judged.
                 if (nested.Judged)
@@ -122,8 +120,7 @@ public void PostProcessHeadJudgement(DrawableSliderHead head)
 
             foreach (var nestedObj in slider.NestedHitObjects)
             {
-                var nested = nestedObj as DrawableOsuHitObject;
-                if (nested == null) continue;
+                if (nestedObj is not DrawableOsuHitObject nested) continue;
 
                 // Skip nested objects that are already judged.
                 if (nested.Judged)