Row-level intersects() filtering via optional WKB-decoder dependency

[gunnarmorling]

Follow-up to #173 (geospatial statistics + bbox-only intersects pushdown).

Context

The intersects(column, xmin, ymin, xmax, ymax) predicate added in #173
performs bbox-only pushdown at the row group and page level, then returns
every surviving row to the caller. The reader does not decode the per-row
WKB payload, so:

• Rows whose individual geometry falls outside the query bbox are still
  emitted (false positives at the row level).
• FilterPredicate.not(intersects(...)) is rejected at resolve time —
  correct per-row evaluation would require decoding every WKB.

This is a deliberate trade-off: it keeps the runtime dependency-free
(arithmetic on the doubles already in the footer / column index).

Proposal

Add opt-in row-level evaluation that decodes the per-row WKB only when
a geometry library is on the classpath, mirroring how the existing optional
compression codecs (snappy-java, zstd-jni, lz4-java, brotli4j) are wired in
core/pom.xml (<optional>true</optional>).

Likely shape:

• A small GeometryDecoder SPI inside dev.hardwood.internal.geo with a
  default no-op implementation. The implementation is selected via
  ServiceLoader (or a classpath probe) at reader construction time.
• A JTS-backed implementation shipped as a separate optional artifact
  (hardwood-geo-jts or core with org.locationtech.jts:jts-core as
  <optional>true</optional>), so users who don't need exact filtering pay
  nothing.
• RecordFilterEvaluator / RecordFilterCompiler: when the decoder is
  available, replace the unconditional true for GeospatialPredicate
  with a real WKB-decode + envelope/intersection test against the query
  bbox.
• Resolver: drop the UnsupportedOperationException for
  not(intersects(...)) once row-level evaluation is wired up. The
  chunk-level dual (containment instead of overlap) can then be added in
  RowGroupFilterEvaluator / PageFilterEvaluator for completeness, but
  is independent of this change.

Out of scope

• Adding new spatial predicates (within, contains, distance).
• 3D / Z-M filtering — initial predicate stays 2D.
• Custom CRS reprojection — query and column CRS are assumed to match.

Acceptance criteria

• With jts-core on the test classpath, an intersects query returns
  only rows whose decoded geometry actually intersects the query bbox
  (verified by an end-to-end test that builds row groups straddling the
  query box).
• Without any geometry library on the classpath, behavior is unchanged
  from Support geospatial statistics and bounding box metadata #173 (bbox-only pushdown, every surviving row returned, negation
  still rejected).
• No mandatory new runtime dependency for core.
• Docs (docs/content/usage.md) updated to describe the opt-in.

References

• Design doc: _designs/GEOSPATIAL_SUPPORT.md (status: implemented for the
  bbox-only layer in Support geospatial statistics and bounding box metadata #173)
• Original PR: Support geospatial statistics and bounding box metadata #173
• Optional-dependency precedent: core/pom.xml snappy/zstd/lz4/brotli4j
  blocks