Feature/winternitz ots

[dilaraacetin]

Fixes #7620

What does this PR add?

This PR adds a Winternitz One-Time Signature (WOTS) implementation, the
size-optimized evolution of the recently added Lamport signature and the actual
building block of modern post-quantum signature standards such as XMSS (RFC 8391)
and SPHINCS+ (FIPS 205).

Implementation details

• WinternitzSignature.java — self-contained, no external dependencies
  (java.security.MessageDigest + SecureRandom only)
• Supports Winternitz parameter w ∈ {4, 16, 256} (default 16); chain counts
  len1, len2, len are derived from w rather than hard-coded
  (e.g. w=16 → len1=64, len2=3, len=67)
• Base-w digit extraction and checksum computation shared between sign and
  verify via a single helper to guarantee symmetry
• One-time property enforced: signing a second message with the same key pair
  throws IllegalStateException
• Defensive copies of all key and signature material; input validation for
  null/malformed inputs and unsupported w values

Tests

WinternitzSignatureTest.java covers: valid signature verification for each
supported w (parameterized), chain-count derivation, tampered message and
tampered signature rejection, wrong key pair and mismatched w rejection,
one-time enforcement, null/invalid inputs, empty and multi-KB messages, and
immutability of returned key material.

Javadocs explain the algorithm, the role of the Winternitz parameter and the
checksum, why the scheme is quantum-resistant, the one-time limitation, and
include a @see reference to LamportSignature plus a Wikipedia link. The
implementation is for educational purposes only.

---

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.46835% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.49%. Comparing base (d291e7d) to head (a0597b3).

Files with missing lines	Patch %	Lines
...com/thealgorithms/ciphers/WinternitzSignature.java	97.46%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7621      +/-   ##
============================================
+ Coverage     81.46%   81.49%   +0.03%     
- Complexity     8053     8079      +26     
============================================
  Files           835      836       +1     
  Lines         25387    25466      +79     
  Branches       4950     4966      +16     
============================================
+ Hits          20681    20754      +73     
- Misses         3921     3924       +3     
- Partials        785      788       +3     

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[alxkm]

Looks good. Thank you for the contribution.