Optimize reading MSeed data

Some timing data:

Data set	Before	After
5083.sdr	221.60537825	144.576911
Centaur_DataTest.nan	205.62063725000004	129.99725875000001
CentaurDiskSOH600.nan	61.81063525000002	40.18216950000004
Pegasus_KCT06_Test.nan	52.7944435	37.40410125
Pegasus_SVC4.nan	10.444169249999998	7.089985750000039