Optimize reading RT130 data

Some tests on large data sets:

	Old code	New code
9BB3_D1.cf	156.14s	32.83s
2016174.9AC4	62.38s	13.61s

Some tests on single files:

	Old code	New code
9BB3_D1.cf/2016326/9BB3/0/000000000_00000000	0.00287s	0.00135s
9BB3_D1.cf/2016327/9BB3/1/030000000_0036EE80	0.177s	0.033s
2016174.9AC4/2016187/9AC4/9/053550000_013EE8A0	0.0026s	0.0013s

tests/model/reftek_data/reftek_reader/test_core.py

@@ -11,7 +11,7 @@ from obspy.io.reftek.packet import PACKET_FINAL_DTYPE
 from sohstationviewer.model.reftek_data.reftek_reader import soh_packet
 from sohstationviewer.model.reftek_data.reftek_reader.core import (
     DiscontinuousTrace,
-    Reftek130,
+    DecimatedReftek130,
 )
 from tests.base_test_case import BaseTestCase