feat: add Iceberg v3 type definitions

[zhjwpku]

Introduce the Iceberg v3 types (variant, geometry, geography), including their schema/JSON serialization and type-system integration (visitors, schema projection, etc.).

Reading and writing data of these types is not implemented yet: conversion to/from Arrow, Avro, and Parquet returns an error, as do identity transform binding and scalar validation for them.

[WZhuo]

LGTM

[Copilot]

Pull request overview

This PR introduces Iceberg v3 type-system support by adding the new types variant, geometry, and geography (plus EdgeAlgorithm for geography), and wiring them through the existing visitor/type utilities, schema/JSON parsing & serialization, and compatibility checks. Data read/write support for these types is explicitly not implemented yet (Arrow/Avro/Parquet conversions and identity transform binding return errors).

Changes:

• Add v3 TypeIds (kVariant, kGeometry, kGeography) and corresponding Type implementations (including CRS/edge algorithm handling and stringification).
• Integrate v3 types into visitors, schema projection/utilities, transforms, and format-version gating; return NotSupported for unsupported IO/conversions.
• Extend and adjust unit tests to cover v3 type parsing/printing and “unsupported” behavior in conversions/transforms.

Reviewed changes

Copilot reviewed 28 out of 28 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
src/iceberg/util/visitor_generate.h	Extends generated visitor action lists and adds explicit dispatch for variant in “primitive default” switch.
src/iceberg/util/visit_type.h	Updates categorical visitor docs to include a fifth category for variant.
src/iceberg/util/type_util.h	Adds VariantType overloads to schema/type utility visitors.
src/iceberg/util/type_util.cc	Implements VariantType visitor handling and adjusts projection logic to treat non-nested leaf types consistently.
src/iceberg/util/struct_like_set.cc	Returns NotSupported for scalar validation of v3 types.
src/iceberg/update/update_schema.cc	Adds VisitVariant handling in schema-update visitor.
src/iceberg/type.h	Adds VariantType, GeometryType, GeographyType, factories, and edge-algorithm APIs; updates type factory group docs.
src/iceberg/type.cc	Implements v3 type behavior, factories, TypeId/EdgeAlgorithm string conversions and parsing.
src/iceberg/type_fwd.h	Adds new TypeIds, EdgeAlgorithm, and forward declarations for new types.
src/iceberg/transform.cc	Disables identity transform for geometry/geography.
src/iceberg/transform_function.cc	Enforces identity-transform input-type restrictions for geometry/geography.
src/iceberg/test/visit_type_test.cc	Extends type test cases to include v3 types and updates nested-vs-non-nested expectations.
src/iceberg/test/type_test.cc	Extends type test cases, adjusts nested checks, and adds geography default/algorithm equality tests.
src/iceberg/test/transform_test.cc	Adds coverage ensuring identity transform rejects v3 types.
src/iceberg/test/schema_test.cc	Adds schema projection test coverage for variant fields.
src/iceberg/test/schema_json_test.cc	Adds JSON round-trip and invalid-input tests for v3 type strings (case/spacing/algorithms).
src/iceberg/test/rest_json_serde_test.cc	Updates expected error message to match new “Cannot parse type string” behavior.
src/iceberg/test/arrow_test.cc	Adds test asserting Arrow conversion rejects v3 types.
src/iceberg/table_metadata.h	Gates v3 types behind Iceberg format version >= 3.
src/iceberg/schema_internal.cc	Refactors Arrow schema conversion to return Status, improves error reporting with type paths, and rejects v3 types explicitly.
src/iceberg/parquet/parquet_writer.cc	Adds VisitVariant to metrics collector visitor.
src/iceberg/parquet/parquet_schema_util.cc	Rejects reading v3 types from Parquet schema evolution validation.
src/iceberg/parquet/parquet_metrics.cc	Adds VisitVariant to metrics visitor.
src/iceberg/metrics_config.cc	Treats variant as a non-nested leaf for metrics field-id limiting.
src/iceberg/json_serde.cc	Adds JSON serialization and parsing for v3 types (including CRS and edge algorithm); normalizes primitive parsing to be case-insensitive.
src/iceberg/delete_file_index.cc	Adjusts equality-delete bound conversion to skip any non-primitive types (avoids mis-casting variant).
src/iceberg/avro/avro_schema_util.cc	Rejects writing/reading v3 types to/from Avro with NotSupported.
src/iceberg/avro/avro_schema_util_internal.h	Declares Avro visitor overloads for v3 types.

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[wgtmac]

Thanks @zhjwpku for adding this and @evindj @WZhuo for the review!