[build] Enable spotbugs (#3601)

Benign spotbugs warnings were suppressed, and all others were fixed. Bug
descriptions are documented here:
https://spotbugs.readthedocs.io/en/stable/bugDescriptions.html

Co-authored-by: Austin Shalit <austinshalit@gmail.com>

wpimath/src/main/java/edu/wpi/first/math/StateSpaceUtil.java

@@ -13,6 +13,8 @@ import org.ejml.simple.SimpleMatrix;
 
 @SuppressWarnings("ParameterName")
 public final class StateSpaceUtil {
+  private static Random rand = new Random();
+
   private StateSpaceUtil() {
     // Utility class
   }
@@ -49,8 +51,6 @@ public final class StateSpaceUtil {
    * @return White noise vector.
    */
   public static <N extends Num> Matrix<N, N1> makeWhiteNoiseVector(Matrix<N, N1> stdDevs) {
-    var rand = new Random();
-
     Matrix<N, N1> result = new Matrix<>(new SimpleMatrix(stdDevs.getNumRows(), 1));
     for (int i = 0; i < stdDevs.getNumRows(); i++) {
       result.set(i, 0, rand.nextGaussian() * stdDevs.get(i, 0));

wpimath/src/main/java/edu/wpi/first/math/filter/MedianFilter.java

@@ -57,13 +57,13 @@ public class MedianFilter {
     // and remove from ordered list
     if (curSize > m_size) {
       m_orderedValues.remove(m_valueBuffer.removeLast());
-      curSize = curSize - 1;
+      --curSize;
     }
 
     // Add next value to circular buffer
     m_valueBuffer.addFirst(next);
 
-    if (curSize % 2 == 1) {
+    if (curSize % 2 != 0) {
       // If size is odd, return middle element of sorted list
       return m_orderedValues.get(curSize / 2);
     } else {

wpimath/src/main/java/edu/wpi/first/math/kinematics/SwerveModuleState.java

@@ -5,6 +5,7 @@
 package edu.wpi.first.math.kinematics;
 
 import edu.wpi.first.math.geometry.Rotation2d;
+import java.util.Objects;
 
 /** Represents the state of one swerve module. */
 @SuppressWarnings("MemberName")
@@ -29,17 +30,30 @@ public class SwerveModuleState implements Comparable<SwerveModuleState> {
     this.angle = angle;
   }
 
+  @Override
+  public boolean equals(Object obj) {
+    if (obj instanceof SwerveModuleState) {
+      return Double.compare(speedMetersPerSecond, ((SwerveModuleState) obj).speedMetersPerSecond)
+          == 0;
+    }
+    return false;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(speedMetersPerSecond);
+  }
+
   /**
    * Compares two swerve module states. One swerve module is "greater" than the other if its speed
    * is higher than the other.
    *
-   * @param o The other swerve module.
+   * @param other The other swerve module.
    * @return 1 if this is greater, 0 if both are equal, -1 if other is greater.
    */
   @Override
-  @SuppressWarnings("ParameterName")
-  public int compareTo(SwerveModuleState o) {
-    return Double.compare(this.speedMetersPerSecond, o.speedMetersPerSecond);
+  public int compareTo(SwerveModuleState other) {
+    return Double.compare(this.speedMetersPerSecond, other.speedMetersPerSecond);
   }
 
   @Override