MINIFICPP-2712 Generate modular docs

[martinzink]

With this PR, ./minifi --docs <output_dir> will generate additional md files one per extension <output_dir>/modules

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[Copilot]

Pull request overview

This PR refactors the documentation generation code to support modular documentation in addition to the existing monolithic documentation. The refactoring moves procedural code into two classes (MonolithDocumentation and ModularDocumentation) to better separate concerns and introduce the new modular documentation feature.

Changes:

• Refactored documentation generation from procedural to class-based approach with MonolithDocumentation and ModularDocumentation classes
• Added support for generating per-module documentation files in a modules/ subdirectory
• Applied code formatting improvements (brace placement, range-based for loop spacing) to comply with .clang-format settings

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