Insure that HitParser returns perfectly sorted packets

[peter-madigan]

Commit 11a188d97b80a7ffbf67f6c18b9fc71152725022 implements a test for this.

• Testing on file datalog_2018_04_15_13_27_44_CEST_.h5.
• Tested sorting on first 10000 hits with sort_buffer_length of 100.
• Passed.

[peter-madigan]

Repeated with 100,000 hits and it fails to sort correctly on 133 packets.

[peter-madigan]

Further inspection of the file shows that there are some chunks of high rate data in which large numbers of packets are generated with very small differences in time (likely a bad channel that then fills the chips' fifo). This can be simply overcome by increasing the sorted buffer to ~2000 hits at the cost of performance. This has been tested successfully on first 100,000 hits of datalog_2018_04_15_13_27_44_CEST_.h5. In the future, we may want to consider fixing this more permanently (e.g. preprocess files with a sorting algorithm).