Format large numbers in a more readable way. (#2046)

- In the bottom line of the TUI, print the number of tokens to 3 sigfigs
  with an SI suffix, e.g. "1.23K".
- Elsewhere where we print a number, I figure it's worthwhile to print
  the exact number, because e.g. it's a summary of your session. Here we print
  the numbers comma-separated.

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -26,6 +26,7 @@ use codex_core::protocol::TurnAbortReason;
 use codex_core::protocol::TurnDiffEvent;
 use codex_core::protocol::WebSearchBeginEvent;
 use codex_core::protocol::WebSearchEndEvent;
+use codex_protocol::num_format::format_with_separators;
 use owo_colors::OwoColorize;
 use owo_colors::Style;
 use shlex::try_join;
@@ -194,7 +195,7 @@ impl EventProcessor for EventProcessorWithHumanOutput {
                     ts_println!(
                         self,
                         "tokens used: {}",
-                        usage_info.total_token_usage.blended_total()
+                        format_with_separators(usage_info.total_token_usage.blended_total())
                     );
                 }
             }