[TRT EP] Fix `trt_load_user_initializer` for large models where weight are not correctly excluded (#25502)
### Description
This change respects initializers that are external but already loaded
in memory. This is required due to an optimization that leaves it to the
backend to read a mapped memory area.
@chilo-ms can you help run the CI and merge this change ?
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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>