[4.2.2] Perform early duplicate detection & fix bugs

New features

• Added word duplication check earlier. (Just press Enter after entering a word)

Feature changes

• Changed the quiz to adjust the problem in units of 1. (Previously 5 units)

• Changed the word creation time in the wordbook to be displayed up to seconds.

• Improved the search window to be focused when the search input field delete button is pressed.

Bug fixes

• Fixed the issue where Google Sheets would not load if the last column was empty.

• Fixed the vocabulary count to be displayed correctly when loading Google Sheets or CSV files.