Add ja4l_delta and ja4ls_delta derived fields to JA4 wireshark plugin

[vlvkobal]

This PR adds two numeric fields to the JA4 Wireshark dissector:

• ja4.ja4l_delta = ja4l_c / ja4l_a
• ja4.ja4ls_delta = ja4ls_c / ja4ls_a

They are computed only when the _c value is numeric and exported for use in filters, columns, and JSON output.

Example (tshark):

ja4.ja4l = 2177_64_114732
ja4.ja4l_delta = 52.7
ja4.ja4ls = 781_238_9107
ja4.ja4ls_delta = 11.7

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Also includes a minor documentation update mentioning JA4D.