[mazkev]

Description of Change

Fixes #480

This PR addresses the open issue #480 ("Add FuzzXxx tests to cipher algorithms") by adding fuzz testing to the Rail Fence cipher, alongside fixing Unicode support and edge case handling:

1. Fuzz Testing (FuzzRailfence):
   • Implemented native Go fuzz test with UTF-8 input validation.
   • Tested through 190,000+ random fuzz iterations without failure.
2. Full Unicode / Multibyte Support:
   • Refactored Encrypt and Decrypt to operate on []rune rather than raw string byte indices. Multibyte characters (e.g. non-Latin scripts, emojis) are now encrypted and decrypted correctly.
3. Null Byte Preservation & Optimization:
   • Replaced sparse 2D matrix allocation with dynamic row slices.
   • Eliminates the previous issue where null bytes (\x00) were filtered out and lost during encryption.
4. Edge Case Safety:
   • Added guards for rails <= 1 or rails >= len(runes) to prevent runtime panics when non-positive rails are provided.

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - GoDoc guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes: Adds FuzzRailfence, Unicode support, and edge-case safety for rail fence cipher.

[codacy-production]

Not up to standards ⛔

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