tests: cover EDA event queue edge cases

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Risky behavior now covered

• EDA disabled gating, channel validation, case-insensitive channel reuse, auto-registration, null payload handling, FIFO drain/peek/pop behavior, channel capacity, payload truncation, full queue overflow rejection, full-ring wraparound, and queue-depth telemetry.
• Fixes the ring-buffer full-queue condition so a valid full queue (s_qHead == s_qTail with s_qCount == EDA_MAX_QUEUE) remains readable.

Test files added/updated

• tests/unit/test_eda.c
• CMakeLists.txt
• tests/README.md
• src/game/g_eda.c (minimal bug fix exposed by the regression test)

Why this reduces regression risk

• EDA is a shared gameplay-facing event path used by Lua/AIML/ECS integration. These tests exercise data validation and queue edge cases that can silently drop events or break integrations.

Validation

• cmake -S . -B build-coverage-tests -DBUILD_TESTING=ON -DBUILD_UNIT_TESTS=ON
• cmake --build build-coverage-tests --target unit_eda && ctest --test-dir build-coverage-tests -R unit_eda --output-on-failure