Capture rollout budget units from response usage (#36641)

## What changed

- Parse `codex_rollout_budget_units` from completed Responses API usage into
  `TokenUsage`.
- Keep the provider-only value out of serialized protocol, JSON schema, and
  TypeScript representations.

## Testing

- Cover the value in unit and end-to-end SSE response parsing tests.

GitOrigin-RevId: a53d4202beb9c8985d25894cb10e7c01f20b2a44

codex-rs/memories/write/src/phase1.rs

@@ -830,6 +830,7 @@ mod tests {
                     output_tokens: 3,
                     reasoning_output_tokens: 1,
                     total_tokens: 13,
+                    codex_rollout_budget_units: None,
                 }),
             },
             JobResult {
@@ -841,6 +842,7 @@ mod tests {
                     output_tokens: 2,
                     reasoning_output_tokens: 0,
                     total_tokens: 9,
+                    codex_rollout_budget_units: None,
                 }),
             },
             JobResult {
@@ -862,6 +864,7 @@ mod tests {
                 output_tokens: 5,
                 reasoning_output_tokens: 1,
                 total_tokens: 22,
+                codex_rollout_budget_units: None,
             })
         );
     }