Track prompt cache write token usage (#33454)

## What changed

- Parse `cache_write_tokens` from response input token details and carry it through token usage aggregation.
- Expose `cache_write_input_tokens` in protocol, app-server, exec, and TypeScript SDK usage events, defaulting it to zero for compatibility with older payloads.
- Report cache-write usage in analytics, metrics, traces, and rollout data alongside existing cache-read usage.

## Testing

- Add coverage for response parsing, usage event output, aggregation, analytics, metrics, and telemetry fields.

GitOrigin-RevId: 634e4fbe3086a8923c0ee13b622573e7d9d221bd

codex-rs/core/src/guardian/metrics.rs

@@ -60,6 +60,10 @@ fn emit_guardian_token_usage_histograms(
         ("total", token_usage.total_tokens.max(0)),
         ("input", token_usage.input_tokens.max(0)),
         ("cached_input", token_usage.cached_input()),
+        (
+            "cache_write_input",
+            token_usage.cache_write_input_tokens.max(0),
+        ),
         ("non_cached_input", token_usage.non_cached_input()),
         ("output", token_usage.output_tokens.max(0)),
         (
@@ -348,6 +352,7 @@ mod tests {
             token_usage: Some(TokenUsage {
                 input_tokens: 10,
                 cached_input_tokens: 4,
+                cache_write_input_tokens: 2,
                 output_tokens: 3,
                 reasoning_output_tokens: 2,
                 total_tokens: 15,
@@ -399,6 +404,7 @@ mod tests {
             histogram_sums(&snapshot, GUARDIAN_REVIEW_TOKEN_USAGE_METRIC),
             BTreeMap::from([
                 ("cached_input".to_string(), 4),
+                ("cache_write_input".to_string(), 2),
                 ("input".to_string(), 10),
                 ("non_cached_input".to_string(), 6),
                 ("output".to_string(), 3),

codex-rs/core/src/guardian/review_session.rs

@@ -128,6 +128,8 @@ fn token_usage_delta(start: &TokenUsage, end: &TokenUsage) -> TokenUsage {
     TokenUsage {
         input_tokens: (end.input_tokens - start.input_tokens).max(0),
         cached_input_tokens: (end.cached_input_tokens - start.cached_input_tokens).max(0),
+        cache_write_input_tokens: (end.cache_write_input_tokens - start.cache_write_input_tokens)
+            .max(0),
         output_tokens: (end.output_tokens - start.output_tokens).max(0),
         reasoning_output_tokens: (end.reasoning_output_tokens - start.reasoning_output_tokens)
             .max(0),
@@ -1636,6 +1638,7 @@ mod tests {
         let start = TokenUsage {
             input_tokens: 10,
             cached_input_tokens: 8,
+            cache_write_input_tokens: 8,
             output_tokens: 6,
             reasoning_output_tokens: 4,
             total_tokens: 28,
@@ -1643,6 +1646,7 @@ mod tests {
         let end = TokenUsage {
             input_tokens: 15,
             cached_input_tokens: 7,
+            cache_write_input_tokens: 7,
             output_tokens: 10,
             reasoning_output_tokens: 2,
             total_tokens: 34,
@@ -1653,6 +1657,7 @@ mod tests {
             TokenUsage {
                 input_tokens: 5,
                 cached_input_tokens: 0,
+                cache_write_input_tokens: 0,
                 output_tokens: 4,
                 reasoning_output_tokens: 0,
                 total_tokens: 6,