Arm backend: Bump to 2026.05 release of tosa-tools

[per]

Summary

Bump the release to 2026.05 and enable the compatibility flag for the serialization to make current and older versions of model-converter being able to deserialize the resulting flatbuffer file.

Test plan

Tested through existing CI.

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

[pytorch-bot]

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✅ You can merge normally! (1 Unrelated Failure)

As of commit c3fe552 with merge base 0d5192c ():

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (trunk failure)

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[Copilot]

Pull request overview

Bumps the Arm backend’s tosa-tools dependency to the 2026.05 release and introduces a tosa_dev_mode compile spec flag to enable experimental/dev-version serialization for improved (de)serialization compatibility across tooling versions.

Changes:

• Bump tosa-tools from 2026.2.1 to 2026.5.0 in Arm/VGF dependency sets.
• Add tosa_dev_mode to ArmCompileSpec, propagate it through compile-spec filtering, and enable it by default for VgfCompileSpec.
• Add the TOSA 1.1 FlatBuffers schema (tosa_1.1.fbs) and add a unit test ensuring tosa_dev_mode round-trips through compile spec serialization.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pyproject.toml	Bumps tosa-tools version in the vgf optional dependency set.
backends/arm/requirements-arm-tosa.txt	Bumps pinned tosa-tools version for Arm TOSA requirements.
backends/arm/common/arm_compile_spec.py	Adds tosa_dev_mode field, (de)serialization support, and setter helper.
backends/arm/vgf/compile_spec.py	Enables tosa_dev_mode by default for VGF compile specs.
backends/arm/tosa/backend.py	Uses tosa_dev_mode to switch serializer into experimental/dev version mode; propagates flag in filter_tosa_compile_specs.
backends/arm/test/misc/test_compile_spec.py	Adds a round-trip test for tosa_dev_mode on VgfCompileSpec.
backends/arm/tosa/schemas/tosa_1.1.fbs	Adds the TOSA 1.1 FlatBuffers schema file.

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