Serialize/flatbuffer to program

[chizkiyahu]

exir: add flatbuffer-to-program reader

This continues the work from #17333.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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[chizkiyahu]

@pytorchbot label "partner: arm"

[chizkiyahu]

@pytorchbot label "release notes: exir"

[chizkiyahu]

@pytorchbot label ciflow/trunk

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[Copilot]

Pull request overview

This PR extends the EXIR serialization stack by adding a direct FlatBuffers → Python Program reader and updating deserialization/tests to use it, continuing the move away from JSON/flatc roundtrips introduced in #17333.

Changes:

• Add _flatbuffer_to_program() to deserialize FlatBuffer bytes directly into executorch.exir.schema.Program dataclasses.
• Switch deserialize_pte_binary() and related tests to use the new direct reader.
• Remove the legacy JSON/flatc conversion helpers and their associated tests.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
exir/_serialize/_flatbuffer_program.py	Adds direct FlatBuffers unpack-to-dataclass conversion (including generated-module alias patching) via _flatbuffer_to_program().
exir/_serialize/_program.py	Updates deserialize_pte_binary() to use _flatbuffer_to_program() instead of FlatBuffer→JSON→dataclass conversion.
exir/_serialize/_flatbuffer.py	Removes JSON/flatc Program conversion helpers that are no longer referenced.
exir/_serialize/test/test_program.py	Updates segment-peek tests to use _flatbuffer_to_program() and adds a richer-type deserialization test.
exir/_serialize/test/test_flatbuffer_program.py	Simplifies roundtrip testing to only cover the direct Python path.
exir/_serialize/test/test_flatbuffer.py	Removes tests for the deleted JSON-to-FlatBuffer Program conversion path.

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[Copilot]

Typo in the comment: "implicity" should be "implicitly".

Suggested change

	# this also implicity tests the case where we try parsing the entire
	# this also implicitly tests the case where we try parsing the entire

[chizkiyahu]

@JacobSzwejbka @lucylq
This is a follow-up to #17333.

• Added a flatbuffer-to-program reader
• Removed the JSON program conversion path

Please let me know if part 2 is too much. I made it a separate commit.

Thanks