fix(client): allow execution submission enum layout

[NathanFlurry]

• Allow the private execution submission enum layout under Rust 1.98 clippy.
• Avoid boxing the synchronous completion result and its additional allocation.

[the-company-company]

Co · session: Fix agentos main CI (clippy 1.98 + browserbase types)

• Auto-fix ; feedback on this pull request flows to the session and gets addressed
• Review ; Co reviews new pushes

_{@co <ask> hands Co a task · @co mute pauses · @co archive ends the session}

[the-company-company]

✅ No issues found

_{Reviewed commit 8fd5bbb.}