fix: switch rate limit reset handling to timestamps (#5304)

This change ensures that we store the absolute time instead of relative
offsets of when the primary and secondary rate limits will reset.
Previously these got recalculated relative to current time, which leads
to the displayed reset times to change over time, including after doing
a codex resume.

For previously changed sessions, this will cause the reset times to not
show due to this being a breaking change:
<img width="524" height="55" alt="Screenshot 2025-10-17 at 5 14 18 PM"
src="https://github.com/user-attachments/assets/53ebd43e-da25-4fef-9c47-94a529d40265"
/>

Fixes https://github.com/openai/codex/issues/4761

codex-rs/clippy.toml

@@ -7,3 +7,7 @@ disallowed-methods = [
     { path = "ratatui::style::Stylize::black", reason = "Avoid hardcoding black; prefer default fg or dim/bold. Exception: Disable this rule if rendering over a hardcoded ANSI background." },
     { path = "ratatui::style::Stylize::yellow", reason = "Avoid yellow; prefer other colors in `tui/styles.md`." },
 ]
+
+# Increase the size threshold for result_large_err to accommodate
+# richer error variants.
+large-error-threshold = 256