Fix URL encoding of the last dot in kurarin (#665)

[mashinosatoshi]

Description

Fixes #665

URL encoding and decoding for kurarin currently ignores the state of the bottom-right dot. This happens because kurarin boards always have an odd number of dots, and the bitwise calculation (bd.dots.length >> 1) | 1 evaluates to 1 less than the required encoded length.

This PR updates the calculation to (bd.dots.length + 1) >> 1 (equivalent to Math.ceil(bd.dots.length / 2)) in both encodeKurarin and decodeKurarin to ensure all dots are properly processed.

Changes

• Fix encodeKurarin and decodeKurarin length calculations in src/variety/kurarin.js
• Add a round-trip test test/variety/kurarin_test.js to verify URL encoding for the last two dots

Testing

• Modified test passes locally.
• Run npm run format and npm test without any issues.

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Thanks, this looks good to me!