fix: clear duration display after meta command execution

[eitsupi]

Summary

• Meta commands (:restart, :help, :cd, etc.) no longer leave the previous R command's duration in the prompt
• Added clear_command_duration() method and call it in both REPL loops when a meta command is processed

Before:

R 4.5.2> Sys.sleep(2)
2s R 4.5.2> :restart    # ← "2s" persists
2s R 4.5.2>

After:

R 4.5.2> Sys.sleep(2)
2s R 4.5.2> :restart    # ← duration cleared
R 4.5.2>

Test plan

• Run Sys.sleep(2), confirm 2s appears in prompt
• Run :help, confirm duration is cleared
• Run :restart (cancel with n), confirm duration is cleared
• Run another R command, confirm new duration works correctly

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a prompt UX issue where the {duration} segment (showing the previous R command’s execution time) could incorrectly persist after executing REPL meta commands (e.g., :help, :restart).

Changes:

• Added PromptRuntimeConfig::clear_command_duration() to reset stored command duration.
• Invoked duration clearing after meta command processing in both the standalone REPL loop and the main R ReadConsole loop.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
crates/arf-console/src/repl/state.rs	Adds a runtime-config helper to clear stored last-command duration so {duration} won’t render stale values.
crates/arf-console/src/repl/mod.rs	Calls the new helper after meta command handling in both REPL input paths to prevent stale duration display.

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