Dell: Reject negative ECS stream seeks

[charliec05]

Summary

• reject negative positions in EcsSeekableInputStream.seek
• validate before changing the pending stream position, preserving state after a rejected seek
• add regression coverage that verifies the existing position and subsequent read remain intact

Motivation

The other cloud-backed seekable streams reject negative positions. The ECS implementation instead stored -1 in its pending-position field, where -1 is also the sentinel for "no pending seek." This discarded the prior seek state and could leave the next read without an initialized underlying stream.

Testing

• ./gradlew :iceberg-dell:spotlessApply :iceberg-dell:test

---

AI Disclosure

• Model: GPT-5 (Codex)
• Platform/Tool: OpenAI Codex
• Human Oversight: fully reviewed
• Prompt Summary: Used a detailed, repository-aware prompt to audit seekable stream boundary handling, require a minimal fix, add state-preserving regression coverage, and run the complete affected module test suite.

[charliec05]

Hi @singhpk234, would you be willing to review this focused Dell ECS stream fix? It rejects negative seeks without corrupting the pending stream position, includes regression coverage, and all 42 CI checks pass. Thanks!