chore: Address PR feedback

Author: lqiu96

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/Field.java

@@ -265,7 +265,7 @@ public Builder setPrecision(Long precision) {
      */
     public Builder setTimestampPrecision(Long timestampPrecision) {
       Preconditions.checkArgument(
-          timestampPrecision != 6L || timestampPrecision != 12L,
+          timestampPrecision == 6L || timestampPrecision == 12L,
           "Timestamp Precision must be 6 (microsecond) or 12 (picosecond)");
       this.timestampPrecision = timestampPrecision;
       return this;
@@ -431,6 +431,7 @@ public String toString() {
         .add("maxLength", maxLength)
         .add("scale", scale)
         .add("precision", precision)
+        .add("timestampPrecision", timestampPrecision)
         .add("defaultValueExpression", defaultValueExpression)
         .add("collation", collation)
         .add("rangeElementType", rangeElementType)
@@ -439,7 +440,19 @@ public String toString() {
 
   @Override
   public int hashCode() {
-    return Objects.hash(name, type, mode, description, policyTags, rangeElementType);
+    return Objects.hash(
+        name,
+        type,
+        mode,
+        description,
+        policyTags,
+        maxLength,
+        scale,
+        precision,
+        timestampPrecision,
+        defaultValueExpression,
+        collation,
+        rangeElementType);
   }
 
   @Override

google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/FieldTest.java

@@ -17,6 +17,7 @@
 package com.google.cloud.bigquery;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
@@ -213,6 +214,20 @@ public void testSubFieldWithClonedType() throws Exception {
     Field.of("field", clonedRecord, Field.of("subfield", LegacySQLTypeName.BOOLEAN));
   }
 
+  @Test
+  public void setTimestampPrecisionValues() {
+    Field.Builder builder = Field.newBuilder(FIELD_NAME1, FIELD_TYPE1);
+
+    // Value values: 6L or 12L
+    builder.setTimestampPrecision(6L);
+    builder.setTimestampPrecision(12L);
+
+    assertThrows(IllegalArgumentException.class, () -> builder.setTimestampPrecision(-1L));
+    assertThrows(IllegalArgumentException.class, () -> builder.setTimestampPrecision(0L));
+    assertThrows(IllegalArgumentException.class, () -> builder.setTimestampPrecision(5L));
+    assertThrows(IllegalArgumentException.class, () -> builder.setTimestampPrecision(13L));
+  }
+
   private void compareFieldSchemas(Field expected, Field value) {
     assertEquals(expected, value);
     assertEquals(expected.getName(), value.getName());