Add multiwinner method code from CElect. · kristomu/quadelect@0bf21be

The following actions uses node12 which is deprecated and will be forced to run on node16: ilammy/msvc-dev-cmd@v1.4.1. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

The following actions use a deprecated Node.js version and will be forced to run on node20: ilammy/msvc-dev-cmd@v1.4.1. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

'argument': conversion from 'size_t' to 'int', possible loss of data

'argument': conversion from 'size_t' to '_Ty', possible loss of data

'argument': conversion from 'size_t' to 'int', possible loss of data

'argument': conversion from 'size_t' to 'int', possible loss of data

'=': conversion from 'size_t' to '_Ty', possible loss of data

'argument': conversion from 'size_t' to 'int', possible loss of data

'argument': conversion from 'size_t' to 'int', possible loss of data

'argument': conversion from 'size_t' to 'int', possible loss of data

'=': conversion from 'size_t' to 'int', possible loss of data

'=': conversion from 'size_t' to 'int', possible loss of data

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