Which issue does this PR close?

• Closes Add Spark-compatible Parquet reader #22339.

Rationale for this change

Issue #22339 asks for a Spark-compatible Parquet reader in the datafusion-spark crate, based on functionality that already exists in apache/datafusion-comet. The schema adapter is the central piece of that reader — it rewrites physical expressions at planning time so that column references against the logical (query) schema resolve correctly to the physical (file) schema while preserving Spark's vectorized-reader semantics.

This PR ports that schema adapter into datafusion-spark so DataFusion users can read Parquet files with Spark semantics by plugging a SparkPhysicalExprAdapterFactory into a FileScanConfig.

What changes are included in this PR?

A new parquet feature on datafusion-spark (off by default), exposing:

• SparkPhysicalExprAdapterFactory / SparkPhysicalExprAdapter — implements PhysicalExprAdapterFactory for use via FileScanConfigBuilder::with_expr_adapter.
• SparkParquetOptions with all the version-sensitive flags (allow_type_promotion, return_null_struct_if_all_fields_missing, case_sensitive, use_field_id, ignore_missing_field_id, etc.) and an EvalMode enum.
• spark_parquet_convert — Spark-compatible nested struct/list/map adaptation, INT96 timezone reinterpret, FixedSizeBinary(16) → UUID rendering.
• SparkCastColumnExpr — PhysicalExpr for column-level type adaptation (timestamp micros → millis, nested field-name relabel, fallback to spark_parquet_convert).
• RejectOnNonEmpty — defers type-promotion rejection to runtime so empty Parquet files still pass (SPARK-26709).
• ParquetSchemaError — the four Parquet-relevant error variants from Comet's SparkError (SchemaConvert, MissingFieldIds, DuplicateFieldByFieldId, DuplicateFieldCaseInsensitive).

The full set of Spark vectorized-reader rejection rules is ported, including:

• BINARY column rejection rules (no int → string, no binary → decimal without DecimalLogicalTypeAnnotation).
• Decimal-to-decimal narrowing (isDecimalTypeMatched).
• Integer-to-decimal narrowing (canReadAsDecimal).
• Configurable type-promotion rejection (Spark 3.x rejects INT32→INT64 etc; Spark 4.x allows them).
• Same-Spark-version rejections (long → narrower int, float → int, etc).
• Scalar/complex type-shape mismatch (SPARK-45604).
• Field-id and case-insensitive matching with duplicate detection.

Per-Spark-version behavior

Documented in parquet/mod.rs. Configured via SparkParquetOptions flags:

• allow_type_promotion — Spark 3.x rejects INT32→INT64 / FLOAT→DOUBLE / INT32→DOUBLE; Spark 4.x allows.
• return_null_struct_if_all_fields_missing — flips at SPARK-53535 (Spark 4.1+).
• eval_mode — Spark 4.0 made Ansi the default.
• TimestampNTZ is supported in the schema mapping.

Simplified vs Comet (deliberately)

• Primitive scalar casts stay as DataFusion's CastExpr rather than Comet's full Spark-compatible Cast PhysicalExpr. Spark's rejection rules still apply at the schema-adapter level; only the cast kernel itself is DataFusion's. Adding a Spark-specific Cast PhysicalExpr to datafusion-spark is a separate task.
• Error taxonomy: only the four Parquet-relevant SparkError variants are ported. Comet's full SparkError enum exists for its JNI bridge to the Spark JVM, which is not relevant here.
• HDFS / object-store cache / JSON error serialization: not ported (Comet-specific concerns).

Are these changes tested?

Yes — 27 new tests, all passing (5 unit + 22 integration tests that round-trip Parquet through DataSourceExec). The integration tests cover every rejection rule that has a corresponding test in Comet's schema_adapter.rs:

• BINARY-as-non-string/binary, string-as-int, binary-as-decimal
• Int32-as-narrow-decimal (rejected) / Int32-as-wide-decimal (allowed)
• Int64-as-narrow-decimal, decimal precision/int-precision narrowing
• Decimal widening (allowed sanity check)
• INT64 → narrower int / float, float → int, double → float, int → float
• INT32 / INT64 → date / timestamp without annotations
• Date → Timestamp(LTZ), Timestamp → Date
• Empty file with disallowed widening (SPARK-26709 — passes)
• Non-empty file with disallowed widening (rejected at runtime)
• Unsigned-int round-trip (Iceberg compatibility)
• Case-insensitive duplicate field detection

Total cargo test -p datafusion-spark --features "core parquet" --lib: 253 passed, 0 failed.

Are there any user-facing changes?

Yes — new public API behind the parquet feature on datafusion-spark:

use datafusion_spark::parquet::{
    EvalMode, SparkParquetOptions, SparkPhysicalExprAdapterFactory,
};

let mut options = SparkParquetOptions::new(EvalMode::Legacy, "UTC", false);
options.allow_type_promotion = false; // Spark 3.x

let factory: Arc<dyn PhysicalExprAdapterFactory> =
    Arc::new(SparkPhysicalExprAdapterFactory::new(options, None));

// Plug into FileScanConfigBuilder::with_expr_adapter

No changes to existing APIs; the new module is gated behind the optional parquet feature.

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