feat(Combinatorics/SimpleGraph/Acyclic): define star graphs

[8e7]

Add a new definition starGraph and several key lemmas. Star graphs are a trivial class of tree, often used in constructive proofs regarding trees.

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All lemmas are hand written first, then golfed with the help of Claude Code.

[github-actions]

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[github-actions]

PR summary 2ff88851d5

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ connected_starGraph
+ instance [DecidableEq V] (r : V) : DecidableRel (starGraph r).Adj := by
+ isAcyclic_starGraph
+ isTree_starGraph
+ starGraph
+ starGraph_adj
+ starGraph_center_adj
+ starGraph_center_degree
+ starGraph_not_center_imp_degree_one

You can run this locally as follows

## summary with just the declaration names:
./scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh contains some details about this script.

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No changes to technical debt.

You can run this locally as

./scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[vlad902]

Please mark the review comments 'resolved' once you've addressed them so the next reviewer doesn't think they're still open.