`map`: Checking for duplicates as we go instead of all at once?

[okamsn]

The map command currently uses seq-uniq to remove all duplicate keys in one go from the result of map-pairs. Would it be faster to check each item as we iterate during the loop, instead of doing it all at once?

• It should be faster if we happen to exit the loop early.
• Is it faster if we don't exit early?
  • [x] For long maps?
  • [x] For short maps?

[okamsn]

Testing map of 10, 100, and 1000 entries showed that it was faster in all cases.