Optimize Plugin API to Avoid Passing Full docx Module

Currently, when using plugins in mdast2docx, we must pass the entire docx module (import * as docx from "docx") to plugin functions.

🔗 Related Discussion: [#6](https://github.com/tiny-md/mdast2docx/discussions/6)
🔗 Blocking Issue in docx Library: [dolanmiu/docx#2988](https://github.com/dolanmiu/docx/issues/2988)

Problem:

• This approach increases bundle size unnecessarily.
• Ideally, each plugin should import only the docx components it needs.
• However, due to how docx handles exports, this is not currently possible.

Proposed Solution (Dependent on docx Fix):

• Once [dolanmiu/docx#2988](https://github.com/dolanmiu/docx/issues/2988) is resolved, update the plugin API:
  • Modify the function signatures so plugins do not require the full docx module.
  • Allow plugins to import only the necessary parts of docx.

📌 Next Steps:

• Monitor the upstream issue in docx.
• If a workaround is available, implement it before the official fix.
• Refactor mdast2docx plugins accordingly once the issue is resolved.

Start by monitoring the linked docx#2988 issue and reviewing the current mdast2docx plugin API and related discussion #6; the payload names no source files or tests. Done means the upstream export limitation is resolved or a workaround exists, and plugin signatures no longer require the full docx module.