Add explicit decision/fallback logging in Book.from_isbn

[Copilot]

Book.from_isbn lacked visibility into fallback/error branches, making ISBN lookup/debug flows opaque in production logs. This update adds explicit logs for branch decisions and fallback failures while preserving existing behavior.

• Logging coverage in Book.from_isbn

  • Added an info log when an ISBN-10 input is converted to ISBN-13.
  • Added warning logs when Google Books metadata is missing and execution falls back to Open Library.
  • Added warning logs for Open Library cover lookup failure paths (error status and request exception).

• Log safety hardening

  • Sanitized ISBN values used in the new log lines by escaping CR/LF characters before interpolation to reduce log-injection risk.

• Representative snippet

  def sanitize_log_value(value: str) -> str:
      return value.replace("\r", "\\r").replace("\n", "\\n")
  
  safe_isbn = sanitize_log_value(isbn)
  
  if isbnlib.is_isbn10(isbn):
      logger.info(f"Decision: from-isbn - Converting ISBN-10 to ISBN-13. isbn={safe_isbn}")
      isbn = isbnlib.to_isbn13(isbn)
      safe_isbn = sanitize_log_value(isbn)
  
  ...
  except KeyError:
      logger.warning(f"Failure: from-isbn - Google Books lookup missing data. isbn={safe_isbn}. Falling back to Open Library")

[User0332]

Remove "decision" from the string

[User0332]

delete this, we don't need to sanitize the ISBN