Fix structure of EpLibraryPlugin::Load so that we call Unload on error.

[skottmckay]

Description

Fix structure of EpLibraryPlugin::Load so that we call Unload on any error and not just an exception.
Currently we directly return on error so the Unload is never hit.

Motivation and Context

Cleanup failed load fully.

[Copilot]

Pull request overview

This PR restructures EpLibraryPlugin::Load() to ensure that a partially loaded EP plugin library is cleaned up on any failure (returned error Status as well as exceptions), instead of only on exceptions.

Changes:

• Wraps the library load sequence in an inner lambda so ORT_RETURN_IF_ERROR produces an error Status without returning from Load().
• Adds a unified failure-path cleanup block intended to call Unload() on any non-OK status.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.