Fix generated-column CI segfault

[mindreframer]

Summary

• classify generated-column reads as unsafe on the pinned Turso 0.7.2 engine
• move the enabled generated-column read probe into the existing disposable child-BEAM path
• keep the disabled parser-gate test in the main ExUnit VM
• align the machine-readable capability matrix and report with the observed behavior

Reproduction

I reproduced the linked job in an Ubuntu Noble Docker container with OTP 28.3, Elixir 1.20.1, Rust 1.91.0, and ERL_FLAGS=+sssdio 64.

MIX_ENV=test TURSOX_BUILD=1 mix test --no-compile \
  --seed 580036 --max-cases 8
# exit 139

The failure narrows to test/experimental_capability_test.exs:63: selecting the enabled generated value segfaults the BEAM. The manager force-close errors immediately before the CI crash are expected test output and are not the process-killing operation.

Verification

In the same clean Docker environment:

• the exact linked seed passed 5 consecutive times: 68 passed
• test/experimental_capability_test.exs passed: 6 passed
• bin/qa_check.sh passed, including formatting, warnings-as-errors compilation, ExUnit, Clippy, and Rust tests