Use Field with serializer

[jacobmerson]

Rather than pass data and layouts separately, we update the serializer to directly take the Field&. This does a better job of maintaining consistency with what data we are operating with. Also, it reduces the number of places we expose FieldData, which is really an internal implementation detail that we don't want readily exposed.

[Copilot]

Pull request overview

This PR updates the field serialization API to operate on Field<T>& (layout + data) instead of taking FieldData<T>& and FieldLayout separately, reducing FieldData exposure and keeping serialization consistent with the field’s active layout.

Changes:

• Updated FieldSerializer and XGCFieldSerializer interfaces to accept Field<T>& directly.
• Updated FieldCommunicator to call the new serializer API.
• Consolidated several field serialization tests into a new test_field_serializer.cpp and removed now-redundant per-backend test cases.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/test_xgc_field_data.cpp	Removes XGC-specific serializer test that is moved into the new consolidated serializer test file.
test/test_uniform_grid_field.cpp	Removes uniform-grid serialization test (moved to consolidated serializer tests).
test/test_polynomial_reconstruction_function_space.cpp	Removes polynomial-reconstruction serialization round-trip test (moved to consolidated serializer tests).
test/test_omega_h_lagrange_field.cpp	Removes Omega_h serialization round-trip tests (moved to consolidated serializer tests).
test/test_field_serializer.cpp	Adds consolidated serializer tests covering multiple backends (Omega_h, uniform grid, polynomial reconstruction, XGC).
test/field_test_utils.h	Removes serializer-related helper(s) now replaced by the consolidated test implementation.
test/CMakeLists.txt	Registers the new consolidated serializer test source file in the unit test build.
src/pcms/coupler/serializer/xgc.h	Updates XGC serializer to accept Field<T>& and use the field’s layout/data bundle.
src/pcms/coupler/field_serializer.h	Updates base serializer interface to accept Field<T>& and derive layout from the field.
src/pcms/coupler/field_communicator.hpp	Updates communicator send/receive to use the new serializer API signature.

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