update unipdf version to v4

[sampila]

This pull request updates the codebase to use version 4 of the UniPDF library (unipdf) instead of version 3. The changes involve updating import paths across multiple files and modifying the go.mod file to reflect the new library version. Below is a summary of the most important changes:

Dependency Update:

• Updated go.mod to replace github.com/unidoc/unipdf/v3 with github.com/unidoc/unipdf/v4 and updated related indirect dependencies (unichart from v0.3.0 to v0.4.0). [1] [2]

Import Path Updates:

• Updated all import paths in the codebase to use v4 of the UniPDF library, including modules like common, model, core/security, extractor, annotator, and others. This change spans across multiple files such as internal/cli/const.go, pkg/pdf/decrypt.go, pkg/pdf/encrypt.go, and more. [1] [2] [3] [4] [5] and others)

Specific Module Updates:

• Updated usage of specific UniPDF submodules like creator, render, optimize, contentstream, and license to their v4 versions. These updates ensure compatibility with the new library version. [1] [2] [3] [4] [5]

These changes are essential for leveraging the latest features and improvements in UniPDF v4 while maintaining compatibility across the project.