Optimize VDS operations with r-tree

[mattjala]

Depends on #5800

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Important

Optimize VDS operations using R-tree spatial index, adding new API functions and tests for improved performance.

• Behavior:
  • Introduces R-tree spatial index for optimizing VDS operations in H5Dvirtual.c.
  • Adds H5Pset_dset_use_spatial_tree() and H5Pget_dset_use_spatial_tree() to control R-tree usage.
  • Default behavior uses R-tree for VDS with more than 1000 mappings.
• Implementation:
  • Adds H5RT.c, H5RTprivate.h, and H5RTpkg.h for R-tree implementation.
  • Updates H5Pdapl.c and H5Pdcpl.c to include R-tree properties.
  • Modifies H5Dvirtual.c to integrate R-tree in VDS I/O operations.
• Testing:
  • Adds rtree.c for testing R-tree creation, search, and copy operations.
  • Tests R-tree integration with VDS in test/dsets.c.
  • Verifies R-tree behavior with different dataset access property list settings.

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[jhendersonHDF]

Generally looks good; see remaining comment though