[codex] Add plugin list JSON output

[xl-openai]

Summary

• add --json output to codex plugin list with installed and available arrays
• add --available for JSON output only; using it without --json is rejected
• keep the existing non-JSON table output unchanged
• add CLI coverage for JSON installed/available output and the --available/--json requirement

Validation

• just test -p codex-cli plugin_list
• just fix -p codex-cli
• git diff --check

Note: just fmt ran Rust formatting first, then failed in the Python ruff step because openai-codex-cli-bin==0.132.0 has no wheel for this Linux platform.