Add Spliterator on NodesQuadTree

[mbastian]

This adds the ability to query the quadtree using (parallel) streams.

• An "approximate" mode has been added to speed up performance. In this mode, element retrieval is purely based on quad node intersection, avoiding to test intersection of many objects.
• Edge query has been revamped and extended. We added support for a "global" iterator that directly iterates edges instead of edges within nodes. This is much faster when the visible objects are large. We've put a threshold at 30% of visible nodes. Above that threshold, we use a global iterator.
• Added additional unit tests.

[Copilot]

Pull Request Overview

Adds spliterator support and predicate/approximate querying to the spatial (quadtree) index, introduces multi-node edge iteration, and updates the SpatialIndex API. Also refactors internal quad tree storage from Set to array plus versioning and adjusts configuration defaults (larger capacities).

• Added Node & Edge spliterators (including filtered and approximate variants) and exposed readLock/readUnlock plus approximate query methods in SpatialIndex.
• Reworked quad tree node storage to fixed-size expandable arrays, added versioning and multi-node edge iterators; edge area queries now may return duplicates (tests updated).
• Increased several default storage and spatial index capacity constants.

Reviewed Changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
SpatialIndexImplTest.java	Adjusts expectations for edge queries (now allowing duplicate edges) and adds clear test.
NodesQuadTreeTest.java	Extensive new tests for counts, iterator/spliterator behavior, predicates, approximate queries, edges, and performance scenarios.
GraphGenerator.java	Adds node generation within an optional Rect2D region.
EdgeStoreTest.java	Updates iterator calls with new locking flag; adds multi-node edge iterator tests.
UndirectedDecorator.java	Adapts to new edge iterator signature with locking flag.
SpatialNodeDataImpl.java	Adds array index tracking and clear() helper for quad tree storage.
SpatialIndexImpl.java	Refactors to delegate edge/node area queries directly to NodesQuadTree, adds approximate & predicate-aware methods, locking passthrough, object count accessor.
NodesQuadTree.java	Major refactor: array-based storage, versioning, predicates, approximate search, edge iteration & spliterators, global edge spliterator, counting APIs.
NodeStore.java	Updates edge iterator usage with new signature (locking flag).
GraphViewImpl.java	Uses spatial index predicate-based filtering; exposes approximate queries; delegates boundaries computation to spatial index.
GraphViewDecorator.java	Adapts view-level area queries to new spatial index methods and iterator signature; simplifies boundary retrieval.
GraphStoreConfiguration.java	Increases edge store and spatial index sizing constants; adds config flags for approximate search and iterator threshold.
GraphStore.java	Updates iterator calls with new edgeIterator signature.
EdgeStore.java	Introduces abstract & multi-node edge iterators; propagates spatial index version bumps; adds iterator/spliterator factory changes.
SpatialIndex.java	Expands API (approximate queries, locking methods) and updates documentation (edges may be duplicated).
Rect2D.java	Changes toString format and adds containsOrIntersects utility methods.

Comments suppressed due to low confidence (1)

src/main/java/org/gephi/graph/api/SpatialIndex.java:1

• [nitpick] Exposing explicit readLock()/readUnlock() in the public SpatialIndex API leaks internal locking strategy and invites misuse (e.g., forgotten unlocks). Consider providing higher-level safe streaming helpers or auto-closeable scopes (e.g., try-with-resources) instead, or confine locking to iterator/spliterator implementations.

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