[skip ci] Fix Iceberg REST S3 path regression coverage

[liurenjie1024]

Fixes #15323.

Description

This is a follow-up to #15360 that makes the Iceberg S3 path regression test reliable with a REST catalog.

The test previously constructed the problematic path by overriding write.data.path with the configured warehouse. For a REST catalog, the warehouse value can be a logical identifier rather than a physical S3 location.

The updated test follows test_iceberg_parquet_read_from_url_encoded_path:

• Adds a string containing a raw space as special-case partition data. The value is valid in an S3 object key but invalid in a URI unless encoded.
• Creates an Iceberg table partitioned by that column and lets Iceberg construct the data-file path through its normal partition writer.
• Continues to run only with the REST catalog, where the optimized S3 reader is exercised.
• Verifies the startup-only spark.rapids.perfio.s3.enabled setting through SparkConf instead of querying an executor-initialized PerfIO singleton from the driver.

Testing performed:

• The REST-catalog run completed 184 existing tests successfully; the three new parameterized variants reached table setup and exposed the driver-side PerfIO assertion corrected here.
• python3 -m py_compile integration_tests/src/main/python/iceberg/iceberg_test.py
• git diff --check

A final REST-catalog pipeline rerun is pending.

Checklists

Documentation

• Updated for new or modified user-facing features or behaviors
• No user-facing change

Testing

• Added or modified tests to cover new code paths
• Covered by existing tests
• Not required

Performance

• Tests ran and results are added in the PR description
• Issue filed with a link in the PR description
• Not required

[greptile-apps]

Greptile Summary

Updates the Iceberg REST S3 regression test to create a space-containing partition path through Iceberg’s normal writer and verifies that PerfIO S3 was explicitly enabled in the startup Spark configuration.

• Replaces the warehouse-derived write.data.path override with a partitioned Iceberg CTAS.
• Adds a heavily weighted partition value containing spaces.
• Checks the startup SparkConf before comparing GPU and CPU reads.

Confidence Score: 5/5

The PR appears safe to merge with no actionable correctness or test-reliability issues identified.

The partitioned CTAS matches an existing Iceberg test pattern, the weighted data generator reliably produces the target value, and the REST test launcher explicitly supplies the startup configuration checked by the new assertion.

Important Files Changed

Filename	Overview
integration_tests/src/main/python/iceberg/iceberg_test.py	The revised deterministic test setup follows an established sibling pattern, exercises all configured reader variants, and checks the REST CI startup configuration without introducing an actionable defect.

_{Reviews (1): Last reviewed commit: "Revert unnecessary chagnes" | Re-trigger Greptile}

[liurenjie1024]

We could skip ci since the changed test in this pr will not run in premerge.

[liurenjie1024]

build

[res-life]

LGTM