feat(iceberg_fdw): [WRA-16] add schema evolution support

[burmecia]

What kind of change does this PR introduce?

This PR is to add schema evolution support to the Iceberg FDW and upgrades iceberg-rs from 0.6.0 to 0.8.0.

What is the current behavior?

• Reading an Iceberg table that has undergone schema evolution (e.g. columns added after initial writes) fails with DataInvalid: missing_fields. The 0.6.0 parquet reader does not tolerate data files that predate a newly-added optional column.
• Schema evolution is listed as unsupported in the docs.

What is the new behavior?

• Schema-evolved tables are read correctly. Rows written before a column was added return NULL for that column; rows written after return the actual value — consistent with the Iceberg spec.
• Filter pushdown on evolved columns works as expected.
• The dependency upgrade to iceberg-rs 0.8.0 to support this new feature

Additional context

N/A

[Copilot]

Pull request overview

Adds schema evolution support to iceberg_fdw by upgrading to iceberg-rs 0.8.0 and wiring schema resolution/pushdown/writer changes needed to correctly read evolved Iceberg tables (older rows returning NULL for newly-added optional columns), with accompanying docs and tests.

Changes:

• Upgrade iceberg / catalog crates (and Arrow/Parquet) to newer versions required for schema evolution tolerant reads.
• Add schema selection by schema_id (optional) and adjust predicate pushdown to operate on the resolved schema.
• Extend test/seed data to validate evolved-schema reads and pushdown on newly-added columns.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
wrappers/src/fdw/iceberg_fdw/writer.rs	Adapts to upstream location generator API change (partition key-aware signature).
wrappers/src/fdw/iceberg_fdw/pushdown.rs	Changes pushdown API to accept an explicit Schema, enabling evolution-aware predicate building.
wrappers/src/fdw/iceberg_fdw/mod.rs	Adds SchemaNotFound error variant for explicit schema_id resolution failures.
wrappers/src/fdw/iceberg_fdw/iceberg_fdw.rs	Implements schema_id resolution on scan, updates Arrow schema conversion, upgrades catalog construction, and adjusts writer pipeline for new iceberg-rs APIs.
wrappers/src/fdw/iceberg_fdw/tests.rs	Adds schema evolution integration assertions and validates default-schema behavior when schema_id is dropped.
wrappers/src/fdw/iceberg_fdw/README.md	Bumps FDW version and changelog entry.
wrappers/dockerfiles/s3/iceberg_seed.py	Seeds a schema-evolved Iceberg table used by integration tests.
wrappers/Cargo.toml	Upgrades iceberg/arrow/parquet dependencies to required versions.
docs/catalog/iceberg.md	Documents schema evolution support and removes the prior “unsupported” limitation.
Cargo.lock	Lockfile updates reflecting the dependency upgrades.

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