[TRT EP] Fix trt context memory sharing (#24784)
### Description
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Fixed a TRT context memory sharing bug where the context memory was
assigned to a unique_ptr that was immediately destructed upon leaving
scope.
### 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. -->
The bug seems to be introduced by a refactor work: #15833 :
