Standardize vertex selector parameter name to `vids`

[Copilot]

Functions calculating results per vertex used inconsistent parameter names: nodes, v, or vids. This standardizes all to vids.

Changed functions

nodes → vids:

• ego(), ego_size(), make_ego_graph() (and their neighborhood* aliases)
• constraint()
• alpha_centrality() (including internal helpers alpha.centrality.{dense,sparse})
• power_centrality() (including internal helpers bonpow.{dense,sparse})

v → vids:

• betweenness()
• cocitation(), bibcoupling()
• degree()
• distances()

Example

g <- make_ring(10)

# Before: inconsistent naming
ego(g, nodes = 1:3)
betweenness(g, v = 1:3)

# After: consistent naming
ego(g, vids = 1:3)
betweenness(g, vids = 1:3)

Positional arguments remain unchanged for backward compatibility.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Inconsistent naming of vertex selector parameters</issue_title> <issue_description>Functions that calculate a result for each vertex (or a subset of vertices) typically have a vertex selector parameter, controlling which specific vertices to include.

This parameter is usually called vids, but not always. This issue is to make sure that the naming is consistent across all functions.

Incomplete functions that don't use vids:

• nodes: ego()/neighborhood() and related, constraint(), alpha_centrality(), power_centrality(), ...
• v: betweenness, cocitation, bibcoupling, degree, distances, ...
• vids: closeness, similarity, transitivity, strength, page_rank, induced_subgraph, diversity, knn, eccentricity, ...</issue_description>

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

• Fixes igraph/rigraph#691

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