Equality delete writer should reject invalid equality field IDs

[u70b3]

Apache Iceberg Rust version

main

Describe the bug

EqualityDeleteWriterConfig::new currently allows invalid equality delete field ID configurations:

• an empty equality_ids list
• duplicate equality field IDs
• schema-missing field IDs surfacing through the projector as a generic error instead of a clear writer configuration error

Equality delete files identify rows by one or more equality column values, so an empty equality ID list should be rejected at writer configuration time. Duplicate IDs can also produce an invalid delete schema with repeated projected columns.

To Reproduce

Construct an equality delete writer config with invalid IDs:

EqualityDeleteWriterConfig::new(vec![], schema.clone());
EqualityDeleteWriterConfig::new(vec![1, 1], schema.clone());
EqualityDeleteWriterConfig::new(vec![99], schema.clone());

Before the fix, empty and duplicate IDs are accepted. Missing IDs are rejected later with a less specific projector error.

Expected behavior

EqualityDeleteWriterConfig::new should return ErrorKind::DataInvalid for:

• empty equality ID lists
• duplicate equality field IDs
• equality field IDs that do not exist in the schema

The writer should continue to rely on the existing projector logic for unsupported field types and map/list reachability rules.

Willingness to contribute

I can contribute a fix for this bug independently.