[codex] simplify memory read metrics

[pakrym-oai]

Why

Memory read telemetry currently reconstructs the executable shell command after a tool call finishes. That duplicates shell, login-policy, and cwd resolution owned by the tool handlers, and can diverge from the environment-specific command that unified exec actually ran.

What changed

• Expose the existing restricted shell-script parser directly for raw script text.
• Parse shell_command and exec_command input into plain command argv before classifying memory reads.
• Preserve all-or-nothing safe-command validation for multi-command scripts.
• Remove cwd resolution, shell selection, and the unnecessary async boundary from memory read metric emission.

Testing

• just test -p codex-shell-command
• cargo check -p codex-core

[chatgpt-codex-connector]

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