fix(tui): use shared paste burst interval on Windows (#18914)

## Summary

Fixes #11678 by removing the Windows-specific
`PASTE_BURST_CHAR_INTERVAL` override. Windows now uses the same `8ms`
paste-burst character interval as macOS and Linux, which removes the
extra per-character hold that made fast typing and key repeat feel
delayed on Windows.

The paste-burst heuristic itself is unchanged, and the Windows-specific
active idle timeout remains in place. This PR only restores the shared
character-to-character burst threshold that decides whether adjacent
plain character events are part of a paste.

## Motivation

PR #9348 raised the Windows character interval from `8ms` to `30ms` to
protect the multiline paste behavior tracked in #2137, where pasted
newlines could be interpreted as submits in Windows terminals. That
fixed the paste failure, but it also made ordinary typing visibly laggy
because the TUI waits briefly before flushing a single typed character
while it checks whether a paste burst is forming.

The deployed behavior here is to remove that Windows-only delay and
return to the cross-platform threshold. Manual Windows validation of the
critical VS Code integrated terminal path shows multiline paste still
works with the final `8ms` value, including testing on VS Code
`1.107.0`.

## Testing

- `cargo test -p codex-tui`
- Manual Windows validation in VS Code integrated PowerShell with the
final `8ms` interval

codex-rs/tui/src/bottom_pane/paste_burst.rs

@@ -154,12 +154,7 @@ const PASTE_BURST_MIN_CHARS: u16 = 3;
 const PASTE_ENTER_SUPPRESS_WINDOW: Duration = Duration::from_millis(120);
 
 // Maximum delay between consecutive chars to be considered part of a paste burst.
-// Windows terminals (especially VS Code integrated terminal) deliver paste events
-// more slowly than native terminals, so we use a higher threshold there.
-#[cfg(not(windows))]
 const PASTE_BURST_CHAR_INTERVAL: Duration = Duration::from_millis(8);
-#[cfg(windows)]
-const PASTE_BURST_CHAR_INTERVAL: Duration = Duration::from_millis(30);
 
 // Idle timeout before flushing buffered paste content.
 // Slower paste bursts have been observed in Windows environments.