Feature/update big int

[LordofGhost]

Describe your changes

Update submodule and references to it.

Issue ticket number if there is one

[Copilot]

Pull request overview

This PR updates the RSA implementation to use the operations::BigInt type (and associated submodule/library) in place of the prior Base256 type, aligning the codebase and build system with the updated big-integer dependency.

Changes:

• Replace operations::Base256 with operations::BigInt across key structures, key generation, and serialization/deserialization.
• Update encryption/decryption to operate on operations::BigInt values.
• Update build linkage and docs to reference BigInt instead of Base256.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/keyPair.h	Switch key fields and (de)serialization helpers to operations::BigInt.
src/keyPair.cpp	Update key generation and key (de)serialization codepaths to use operations::BigInt.
src/helper.h	Update include to the new bigint header dependency.
src/encrypt.cpp	Use operations::BigInt for plaintext/ciphertext math.
src/decrypt.cpp	Use operations::BigInt for ciphertext/plaintext math.
docs/algorithms/div.md	Update normalization wording from Base256 to BigInt.
CMakeLists.txt	Link RSA target against BigInt rather than Base256.

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[Jochengehtab]

lgtm