Fix unpacking errors triggered by _embed_annotations in get_bookmarks() and get_highlights() functions

[r7nd7]

Problem

When using the _embed_annotations , users may run into unpacking errors in the get_bookmarks() and get_highlights() functions inside sioyek.py.

These functions expect a fixed number of columns returned by SQLite queries. However, on some systems (e.g., Arch Linux with Python 3.12+), the database may return extra columns due to schema changes or environment-specific differences.

This can trigger errors like:

• ValueError: too many values to unpack (expected 4)
• ValueError: too many values to unpack (expected 8)

These issues break the _embed_annotations feature, which depends on both functions to extract highlights and bookmarks.

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What this PR does

• Replaces fixed unpacking with a more robust pattern that handles extra columns gracefully
• Uses length checks and wildcard unpacking (*_) to capture only the needed fields
• Preserves the original behavior using list comprehensions
• Makes _embed_annotations more reliable across environments

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Testing

• Verified _embed_annotations works correctly after adding highlights and bookmarks
• Tested with Sioyek installed via pip on Python 3.12
• Used a PDF with real annotations to confirm that embed_annotations.py runs successfully

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