nominatimlite 0.6.0

• The minimum required R version is now 4.1.0.
• Documentation has been proofread and aligned across roxygen2 comments, README
  and vignettes with AI assistance.
• Internal code has been refactored with AI assistance to reduce duplication in
  URL construction, progress handling, coordinate validation and output
  preparation without changing the public API.
• User-facing messages have been clarified with AI assistance, including
  unreachable API endpoint messages, capped limit messages and empty
  structured query messages.

What's Changed

• Deep refactor, AI-assisted by @dieghernan in #63

Full Changelog: v0.5.0...v0.6.0