refactor(core): bake single-thread assumptions into spawn/spawn_blocking (#19056)

Partially supersedes #19016.

This migrates `spawn` and `spawn_blocking` to `deno_core`, and removes
the requirement for `spawn` tasks to be `Send` given our single-threaded
executor.

While we don't need to technically do anything w/`spawn_blocking`, this
allows us to have a single `JoinHandle` type that works for both cases,
and allows us to more easily experiment with alternative
`spawn_blocking` implementations that do not require tokio (ie: rayon).

Async ops (+~35%):

Before: 

```
time 1310 ms rate 763358
time 1267 ms rate 789265
time 1259 ms rate 794281
time 1266 ms rate 789889
```

After:

```
time 956 ms rate 1046025
time 954 ms rate 1048218
time 924 ms rate 1082251
time 920 ms rate 1086956
```

HTTP serve (+~4.4%):

Before:

```
Running 10s test @ http://localhost:4500
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    68.78us   19.77us   1.43ms   86.84%
    Req/Sec    68.78k     5.00k   73.84k    91.58%
  1381833 requests in 10.10s, 167.36MB read
Requests/sec: 136823.29
Transfer/sec:     16.57MB
```

After:

```
Running 10s test @ http://localhost:4500
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    63.12us   17.43us   1.11ms   85.13%
    Req/Sec    71.82k     3.71k   77.02k    79.21%
  1443195 requests in 10.10s, 174.79MB read
Requests/sec: 142921.99
Transfer/sec:     17.31MB
```

Suggested-By: alice@ryhl.io
Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/runtime/inspector_server.rs b/runtime/inspector_server.rs
index 25d0d796c..1a6706896 100644
--- a/runtime/inspector_server.rs
+++ b/runtime/inspector_server.rs
@@ -15,6 +15,7 @@ use deno_core::futures::task::Poll;
 use deno_core::serde_json;
 use deno_core::serde_json::json;
 use deno_core::serde_json::Value;
+use deno_core::task::spawn;
 use deno_core::InspectorMsg;
 use deno_core::InspectorSessionProxy;
 use deno_core::JsRuntime;
@@ -109,7 +110,7 @@ where
   Fut::Output: 'static,
 {
   fn execute(&self, fut: Fut) {
-    tokio::task::spawn_local(fut);
+    deno_core::task::spawn(fut);
   }
 }
 
@@ -160,7 +161,7 @@ fn handle_ws_request(
 
   // spawn a task that will wait for websocket connection and then pump messages between
   // the socket and inspector proxy
-  tokio::task::spawn_local(async move {
+  spawn(async move {
     let websocket = if let Ok(w) = fut.await {
       w
     } else {