pre-compute firstByteMaxValue

this operation is executed very often during ingestion

performanceDb/src/main/java/org/lucares/performance/db/ByteType.java

@@ -28,9 +28,11 @@ enum ByteType {
 	}
 
 	private final int firstBytePrefix;
+	private final int firstByteMaxValue;
 
 	private ByteType(final int firstBytePrefix) {
 		this.firstBytePrefix = firstBytePrefix;
+		firstByteMaxValue = firstBytePrefix-1;
 	}
 
 	public int getBytePrefix() {
@@ -48,7 +50,7 @@ enum ByteType {
 	 * @return the maximum value for the first byte of this sequence
 	 */
 	public long getFirstByteMaxValue() {
-		return firstBytePrefix - 1;
+		return firstByteMaxValue;
 	}
 
 	/**