feat: Add distance metric support for RTree neighbor queries (#141)

* feat: Add distance metric support for RTree neighbor queries

  Add pluggable distance metrics for RTree neighbor searches, enabling
  Euclidean, Haversine, and Spheroid distance calculations. This allows
  users to choose appropriate distance calculations for different coordinate
  systems (planar vs geographic).

* fix cargo fmt

* fix clippy fmt

* Address PR review comments

- Feature Flag Implementation (geo-types pattern)
- Removed top-level re-exports from rtree/mod.rs
- Removed redundant geo-types dependency
- Removed duplicate axis_dist function (now in trait.rs)
- Made entire distance module conditional on use-geo_0_31 feature
- Trait architecture change: created SimpleDistanceMetric (no geo dependency)
- Tests run successfully with and without use-geo_0_31 feature flag

* remove the vincenty (Geodesic) and GRS80 distance metrics

Author: zhangfengcdt

.gitignore

@@ -25,3 +25,5 @@ target/
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 /target
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+.idea/