Use `vctrs` for vector recycling

[Copilot]

Replaces manual vector recycling using rep(x, length.out = n) with vctrs::vec_recycle(x, n) for better error messages and consistency.

Changes

• R/plot.R: Use vctrs::vec_size_common() to determine common size in igraph.Arrows(), then recycle all parameters to that size
• R/games.R, R/centrality.R, R/epi.R: Replace rep(..., length.out = ) with vctrs::vec_recycle()
• R/plot.shapes.R, R/plot.common.R, R/tkplot.R, R/sparsedf.R: Same pattern throughout plotting and utility functions

Example

Before:

recycle <- function(x) rep(x, length.out = n)
x1 <- recycle(x1)
y1 <- recycle(y1)

After:

n <- vctrs::vec_size_common(x1, y1, x2, y2)
x1 <- vctrs::vec_recycle(x1, n)
y1 <- vctrs::vec_recycle(y1, n)

This provides clearer error messages when inputs have incompatible sizes and centralizes recycling logic through a well-tested dependency already in use.

Original prompt

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This section details on the original issue you should resolve

<issue_title>use vctrs in more places</issue_title> <issue_description>when there is recycling

e.g. use vctrs::vec_size_common()</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes igraph/rigraph#1249

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[maelle]

@krlmlr for such patterns do we also want to add some linting to prevent future drift?