Move `OrtEp` sanity checks to plugin EP creation and remove check for `OrtEp::ort_version_supported` upper bound (#28601)
### Description
<!-- Describe your changes. -->
- Move OrtEp sanity checks from op kernel creation to EP creation.
- Remove check for upper bound of OrtEp::ort_version_supported.
- Add tests covering sanity checks.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Revert rejection of `OrtEp` instances that specify a version in
`ort_version_supported` larger than ORT's `ORT_API_VERSION`. The
guidance is for plugin EPs to set it to the `ORT_API_VERSION` value from
their ORT header, but plugin EPs may optionally support earlier versions
of ORT as well.
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>