Fix undefined symbol linker error by moving sign and secureHash t…

[ahaladok]

Move template definitions to .h file

Description

Moved the definitions of template methods Signer::sign and Address::secureHash from .cpp to .h files to resolve linker errors due to missing template instantiations. This change ensures that the compiler has access to the full implementation of these templates in the translation units where they are used.

Error was fixed:

Undefined symbols for architecture x86_64: "std::__1::vector<unsigned char, std::__1::allocator<unsigned char>> TW::Waves::Address::secureHash<std::__1::vector<unsigned char, std::__1::allocator<unsigned char>>>(std::__1::vector<unsigned char, std::__1::allocator<unsigned char>> const&)", referenced from: TW::Waves::tests::WavesAddress_SecureHash_Test::TestBody() in AddressTests.cpp.o "void TW::Harmony::Signer::sign<TW::Harmony::Transaction>(TW::PrivateKey const&, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>> const&, TW::Harmony::Transaction&) const", referenced from: TW::Harmony::HarmonySigner_SignAssumeLocalNet_Test::TestBody() in SignerTests.cpp.o ld: symbol(s) not found for architecture x86_64 c++: error: linker command failed with exit code 1 (use -v to see invocation)

How to test

1. Run a full build of the project to ensure that the linker error is resolved and all components compile successfully.
2. Verify functionality by running existing tests for Signer::sign and Address::secureHash.
3. Check for any potential issues with symbol resolution across different platforms (e.g., macOS, Linux).

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Create pull request as draft initially, unless it's complete.
• Add tests to cover changes as needed.
• [х] Update documentation as needed.
• If there is a related Issue, mention it in the description.