API: add column-default model support

[cbb330]

Summary

• Backport the NestedField column-default model (initial-default / write-default) from Apache Iceberg #9502.
• Add Expressions.lit and the SchemaParser JSON round-trip for default literals.
• Pure API/Core change: no reader behavior changes on its own; consumed by the ORC fill PR that stacks on top.

Stack (bottom -> top)

1. ORC: bind struct fields by Iceberg field id in generic and Spark 3.1 readers #256 - ORC id-binding backport (base 1.2.x)
2. this PR - API column-default model (base chbush/orc-id-binding-backport)
3. ORC initial-default fill (base chbush/orc-column-default-api)
4. Spark 3.1 wiring (base chbush/orc-initial-default-orc-fill)

Testing Done

• iceberg-api and iceberg-core suites pass
• SchemaParser round-trip test added
• API/Core RevAPI, checkstyle, and formatting pass

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Made with Cursor

[cbb330]

Closing: this was based on the wrong branch (1.2.x, which is essentially vanilla apache 1.2.x). The correct target is the OpenHouse dev branch openhouse-1.2.0, which already has the id-bound ORC readers and the NestedField column-default API (#250) — so the id-binding and API backports here were redundant.

Rebuilt as a clean 2-PR stack on openhouse-1.2.0:

• ORC: fill initial defaults for missing id-bound fields #263 - ORC: fill initial defaults for missing id-bound fields
• Spark 3.1: fill ORC initial defaults on the row reader #264 - Spark 3.1: fill ORC initial defaults on the row reader