Reduce allocation overhead of no-op `GeospatialStatistics.Builder`

### Describe the enhancement requested

`GeospatialStatistics.noopBuilder()` is called for every non-geometry column in every row group. Today, each call allocates a new `NoopBuilder` (plus a `WKBReader`, `BoundingBox`, and `GeospatialTypes` that are never used), and each `build()` allocates a new `GeospatialStatistics(null, null)` that is immediately discarded.

Since `NoopBuilder` carries no state and all its methods are no-ops, it can be a singleton. Its `build()` result is equally stateless (null fields, with merge/abort guarded by null checks), so it can be cached too.

### Proposed Changes
- Make `NoopBuilder` a singleton via a static `INSTANCE` field
- Cache `build()` output as a static `EMPTY` instance
- Add a package-private super constructor that skips field initialization so the singleton doesn't allocate unused objects

This eliminates per-column-per-row-group allocations on the common path where geospatial statistics are disabled.

### Component(s)

Core

Start at GeospatialStatistics.noopBuilder() and trace NoopBuilder, its build() method, and the relevant constructors. Confirm how unused fields are initialized and verify that the no-op builder and empty statistics result are reused without changing merge or abort behavior; done means the common path no longer allocates those objects per call.

Written by the indexing model from the issue text.