docs: improve docstrings and typespecs

[AlexGx]

This PR focuses on improving documentation clarity and correcting grammatical errors.

Changes

• documentation refinements: fixed numerous typos, grammatical inconsistencies, and phrasing issues in module documentation (Access, Calendar, Code, File, MapSet)
• typespecs: added missing typespecs (Code.Fragment.lines/1) and improved existing ones to better reflect actual implementation logic (MapSet.split_with/2)
• clarification: improved technical explanations for better readability and fix ceil/2 description
• consistency: standardized punctuation and formatting within docstrings to align with project style

[josevalim]

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