Add OpenSSL 4 compatibility and modernize CMake build system

[olszomal]

Pull Request Type

• Bug fix
• New feature
• Code style / formatting / renaming
• Refactoring (no functional or API changes)
• Build / CI related changes
• Documentation
• Other (please describe):

Related Issue

Issue number: N/A

Current Behavior

The project uses direct ASN.1 structure field access, which is deprecated and incompatible with OpenSSL 4.
The CMake build system also lacks integrated documentation generation, GNU install directory support, and an uninstall target.

New Behavior

• use ASN.1 accessor APIs for OpenSSL 4 compatibility
• refactor SpcIndirectDataContent parsing helpers
• reduce duplicated PKCS7 parsing code
• add Pandoc documentation generation and modern CMake install support

Scope of Changes

• OpenSSL compatibility fixes
• ASN.1 and PKCS7 helper cleanup
• CMake packaging and installation improvements

Testing

• Existing tests
• New tests added
• Manual testing

Additional Notes

License Declaration

• I hereby agree to license my contribution under the project's license.