feat: add annotations in MD & HTML serialization

[vagenas]

• included annotations in MD & HTML serialization as default (users can opt out)
  • MD: appended to text
  • HTML: appended to figcaption content
  • (DocTags currently not touched as apparently specialized annotation handling already included there)
  • exposed via param include_annotations in respective DoclingDocument methods
• annotation handling single-sourced in common.py
  • annotation types currently handled: classification, description, & SMILES

Resolves docling-project/docling#1608

[mergify]

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[codecov]

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[dolfim-ibm]

lgtm

[PeterStaar-IBM]

lgtm!

[PeterStaar-IBM]

lgtm!