Fix Iceberg runtime stub in root-safe packaging test [reduced-it]

[res-life]

Fixes the CI regression introduced in #15944.

Description

Add the missing system_runtime_path() stub to the root-safe packaging test's synthetic Iceberg runtime module.

The standard assembler requires this interface after #15957, but the test fixture only provides coordinates(), causing KeyError: 'system_runtime_path' during Maven verification. Returning None models the test's unconfigured system runtime and lets both assembler paths reach the existing placement and deduplication assertions. Production code is unchanged.

Validation:

• env TMPDIR=/home/chongg/codex/tmp/tmp python3 dist/scripts/tests/test_root_safe_provider_selection.py: reproduced the KeyError before the fix; passed after the fix, including standard and fast assembler subtests.
• git diff --check: passed.

AI assistance: prepared with Codex.

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
  (Please provide the names of the existing tests in the PR description.)
• Not required

Performance

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

[res-life]

build

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable issues identified.

Summary

• Adds the missing system_runtime_path(get_property) interface.
• Models an unconfigured system runtime by returning None.
• Leaves production code and runtime performance unchanged.

_{Reviews (1) · Last reviewed commit: "Fix Iceberg runtime stub in root-safe pa..."}

[res-life]

duplicated with #15985