feat: add endnotes support to docx library

[AlabasterAxe]

Summary

• Add comprehensive endnotes implementation with EndnoteReferenceRun component
• Create Endnotes class and EndnotesWrapper for document integration
• Add endnote attributes, reference runs, and separator components
• Update documentation to cover both footnotes and endnotes usage
• Include demo file demonstrating endnotes functionality with multiple sections
• Integrate endnotes into compiler pipeline and content types
• Add comprehensive test coverage for endnote components

Key Features

• EndnoteReferenceRun: Component for adding endnote references in paragraphs
• Endnotes class: Manages endnote content and formatting
• Documentation updates: Extended footnotes.md to cover endnotes usage
• Demo implementation: Complete working example in demo/97-endnotes.ts
• Test coverage: Comprehensive unit tests for all endnote components

Differences from Footnotes

• Endnotes appear at the end of the document, unlike footnotes which appear at the bottom of each page
• Ideal for academic papers, research documents, and lengthy citations
• References automatically appear as superscript in the document

Test plan

• [x] All existing tests pass
• [x] New endnote tests pass
• [x] Demo file generates valid DOCX with endnotes
• [x] Documentation updated with usage examples
• [x] Code follows project formatting and linting standards

Fixes #359

[AlabasterAxe]

@dolanmiu FYI

[dolanmiu]

Thanks @AlabasterAxe

Looks good to me

Edit: Failing tests if you don't mind fixing, and then it can be merged.