feat: add manual and remote_v2 tags to compaction metric (#24608)

## Why
`codex.task.compact` only distinguished `local` vs `remote`, which made
it hard to answer simple counter questions in Statsig. Manual `/compact`
and automatic compaction were collapsed together, and the legacy remote
path was also collapsed with `remote_compaction_v2`.

## What Changed
- route `codex.task.compact` through a shared helper in
`core/src/tasks/mod.rs`
- add a `manual=true|false` tag so manual and automatic compaction can
be counted separately
- split the remote tag into `remote` and `remote_v2`
- emit the metric from the inline auto-compaction path in
`core/src/session/turn.rs` as well as the manual `CompactTask` path in
`core/src/tasks/compact.rs`
- add focused unit coverage for the new tag shapes in
`core/src/tasks/mod_tests.rs`

## Verification
- added unit coverage in `core/src/tasks/mod_tests.rs` covering manual
`remote_v2` tags and automatic `local` tags

codex-rs/core/src/tasks/compact.rs

@@ -2,6 +2,7 @@ use std::sync::Arc;
 
 use super::SessionTask;
 use super::SessionTaskContext;
+use super::emit_compact_metric;
 use crate::session::TurnInput;
 use crate::session::turn_context::TurnContext;
 use crate::state::TaskKind;
@@ -29,24 +30,29 @@ impl SessionTask for CompactTask {
     ) -> Option<String> {
         let session = session.clone_session();
         let _ = if crate::compact::should_use_remote_compact_task(ctx.provider.info()) {
-            session.services.session_telemetry.counter(
-                "codex.task.compact",
-                /*inc*/ 1,
-                &[("type", "remote")],
-            );
             if ctx
                 .features
                 .enabled(codex_features::Feature::RemoteCompactionV2)
             {
+                emit_compact_metric(
+                    &session.services.session_telemetry,
+                    "remote_v2",
+                    /*manual*/ true,
+                );
                 crate::compact_remote_v2::run_remote_compact_task(session.clone(), ctx).await
             } else {
+                emit_compact_metric(
+                    &session.services.session_telemetry,
+                    "remote",
+                    /*manual*/ true,
+                );
                 crate::compact_remote::run_remote_compact_task(session.clone(), ctx).await
             }
         } else {
-            session.services.session_telemetry.counter(
-                "codex.task.compact",
-                /*inc*/ 1,
-                &[("type", "local")],
+            emit_compact_metric(
+                &session.services.session_telemetry,
+                "local",
+                /*manual*/ true,
             );
             let input = vec![UserInput::Text {
                 text: ctx.compact_prompt().to_string(),