Add VIC cipher codec

[Copilot]

Checklist

• No unrelated changes
• Codec is new (not already implemented)
• Tests included (if cannot be automated with tests/test_generated)
• Documentation (included in the right page in docs/pages/enc)

Description

The VIC cipher is a Soviet spy cipher combining a straddling checkerboard substitution with a double columnar transposition. Reference: https://www.dcode.fr/vic-cipher

Checkerboard: A keyword-mixed 26-letter alphabet fills a 3-row grid with blanks at columns 2 and 6. Top-row letters get single-digit codes; the two lower rows get two-digit codes prefixed by their blank-column header — producing a self-synchronising digit stream.

Double transposition: Two independent columnar transpositions are applied sequentially to the digit stream, each driven by its own key.

Codec name: vic-KEYWORD-TRANS1KEY[-TRANS2KEY] — TRANS2KEY defaults to TRANS1KEY when omitted.

>>> codext.encode("HELLO", "vic-python-352")
'42228285'
>>> codext.decode("42228285", "vic-python-352")
'HELLO'
>>> codext.encode("ATTACKATDAWN", "vic-python-352-461")
'8833231882605277'
>>> codext.decode("8833231882605277", "vic-python-352-461")
'ATTACKATDAWN'

Roundtrip tests are covered by __examples__ and exercised automatically via tests/test_generated.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add new encoding: vic</issue_title>
<issue_description>### Description

The VIC cipher is a substitution cipher with an overencryption using transposition, named after a spy called Victor.

Reference

https://www.dcode.fr/vic-cipher</issue_description>

<agent_instructions>Propose an implementation that satisfies the guideline at docs/pages/howto.md.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Add new encoding: vic #35

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