fix(ja4t): align Rust JA4T output with Wireshark/Zeek

[elpy1]

This PR aligns Rust with Wireshark/Zeek on:

• Empty TCP options: emit "00" placeholder instead of an empty field
• Absent MSS / window scale: zero-pad defaults to "00" instead of "0"
  (window scale stays unpadded when nonzero, matching Wireshark)
• Duplicated MSS / window-scale options: last occurrence wins
  instead of first

Still unresolved:

• ECN-flagged SYN behavior (accepted by the Rust implementation
  but ignored by Wireshark/Zeek).

Partially addresses #304

[vlvkobal]

JA4T numeric fields are formatted as decimal values, while 00 is reserved for fields that are absent. The current implementation conflates a missing value with a present value of zero. Could you update the formatting logic and tests to preserve this distinction?

@john-althouse, since this behavior is not currently documented publicly, should we add it somewhere?