API: Treat default edge algorithm as equal to an omitted one in GeographyType

[huan233usc]

Summary

Make Types.GeographyType treat an explicit default edge-interpolation algorithm as equal to an omitted one, so semantically identical geography types compare equal.

GeographyType uses null internally to mean "default" for both crs and algorithm, but equals / hashCode / toString compared the raw nullable fields. As a result GeographyType.of(crs, EdgeAlgorithm.SPHERICAL) was not equals() to the equivalent GeographyType.of(crs), even though SPHERICAL is the documented default and the algorithm() getter resolves to SPHERICAL for both. This also meant a plain geography did not round-trip through format conversions that omit default values — e.g. Parquet's geography logical type, where an unset algorithm defaults to SPHERICAL (#16765).

Rather than collapse the default in the constructor, this normalizes at the comparison/render boundary: equals, hashCode, and toString now use the resolved getters crs() / algorithm(), which already apply the defaults. So an explicit default and an omitted one compare equal and render the same compact form. The constructor is left untouched, and CRS — which already resolved this way through the getter — is brought in line with the algorithm. No public signature changes.

Test plan

• Extended testGeospatialTypeToString to confirm an explicit default SPHERICAL renders the same compact form as an omitted algorithm (geography, geography(srid:4326)).
• New testGeospatialTypeDefaultNormalization covers equals() / hashCode() parity for the default-CRS and default-algorithm forms, that algorithm() still reports SPHERICAL, and that a non-default algorithm (KARNEY) stays distinct.
• ./gradlew :iceberg-api:check — clean (tests, checkstyle, revapi, spotless).
• ./gradlew :iceberg-core:test — full core suite green; no regressions in TestSchemaParser / TestSingleValueParser / TestGeospatialTable / TestSchemaUnionByFieldName or anywhere geography types are serialized.

[huan233usc]

Consolidated into #16765 — the GeographyType equality change and the Parquet schema mapping it enables are now reviewed together there.