Fix edge.width not applied to drawn line widths in nplot

[Copilot]

edge.width values were rescaled correctly inside nplot.default but only set during grob creation in grob_edge.R. The post-processing step that applies col via set_edge_gpar had no equivalent for lwd, making widths unreliable.

Changes

• R/netplot.R — After all color post-processing in nplot.default, explicitly apply rescaled edge.width via set_edge_gpar(lwd = ...) for both "line" and "arrow" elements:

  if (!skip.edges)
    ans <- set_edge_gpar(x = ans, element = "line", lwd = as.vector(netenv$edge.width))
  if (!skip.arrows)
    ans <- set_edge_gpar(x = ans, element = "arrow", lwd = as.vector(netenv$edge.width))

• R/netplot.R — Improved @param docs for edge.width and edge.width.range to clarify normalization and range mapping behavior.
• vignettes/examples.Rmd — Added "Edge width" section demonstrating edge.width, edge.width.range, and post-hoc set_edge_gpar() usage.
• inst/tinytest/test_netplot.R — Test that lwd values retrieved via get_edge_gpar fall within the specified edge.width.range and are monotonically non-decreasing with weight.
• NEWS.md — Changelog entry for the fix.