[razvcris]

Summary

Removes the C++ ETFeeder (src/feeder, tests/feeder) and everything that only existed to support it.

Why

• The feeder has no Python consumer and is not shipped in the wheel.
• ASTRA-sim no longer uses it: it maintains its own feeder, see Migrate et feeder from forked/branched chakra submodule into ASTRA-sim repo astra-sim/astra-sim#385. The src/feeder copy here was only an example for downstream integrations.
• It was still built and tested in CI without any real user.

Changes

• Removed src/feeder, tests/feeder, and tests/data/feeder_tests_trace.tar.gz
• Removed the C++ dependencies only the feeder used: protoio.cc/.hh and json.hpp from src/third_party/utils
• Removed workflows feeder_tests.yml and cpp_lint.yml, plus .clang-format
• Removed the c-cpp job and manual build step from codeql.yml (Python analysis unchanged)
• Removed the ETFeeder section from USER_GUIDE.md

Test plan

• Ran the Python test suite: python -m pytest tests/ - all tests pass
• Searched for leftover references: grep -rIi "feeder\|protoio\|json.hpp\|clang" - no matches

Closes #229, #228

[github-actions]

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[danmih-ixia]

LGTM.