fix(examples): assorted fixes in the async example

[bavshin-f5]

• Use single tokio runtime instance. Move runtime initialization to the worker process.
• Use ngx_posted_next_events to avoid posting events to the tail of currently executed queue.
• Move event and done to the request context, remove EventData.
• Ensure the async task cancellation when the request is aborted.
• Test async example in CI.

feat!: replace Request.get_inner with AsRef/AsMut technically does not belong here, but it's too small to deserve a PR on its own.

[xeioex]

Take a look

diff --git a/examples/async.rs b/examples/async.rs
index 7fe1584f..bb63a0f7 100644
--- a/examples/async.rs
+++ b/examples/async.rs
@@ -7,10 +7,10 @@ use std::time::Instant;
 
 use ngx::core;
 use ngx::ffi::{
-    ngx_array_push, ngx_command_t, ngx_conf_t, ngx_connection_t, ngx_event_t, ngx_http_core_module,
-    ngx_http_core_run_phases, ngx_http_handler_pt, ngx_http_module_t, ngx_http_phases_NGX_HTTP_ACCESS_PHASE,
-    ngx_http_request_t, ngx_int_t, ngx_module_t, ngx_post_event, ngx_posted_next_events, ngx_str_t, ngx_uint_t,
-    NGX_CONF_TAKE1, NGX_HTTP_LOC_CONF, NGX_HTTP_LOC_CONF_OFFSET, NGX_HTTP_MODULE,
+    ngx_add_timer, ngx_array_push, ngx_command_t, ngx_conf_t, ngx_connection_t, ngx_event_t, ngx_http_core_module,
+    ngx_http_handler_pt, ngx_http_module_t, ngx_http_phases_NGX_HTTP_ACCESS_PHASE, ngx_int_t, ngx_module_t,
+    ngx_post_event, ngx_posted_events, ngx_str_t, ngx_uint_t, NGX_CONF_TAKE1, NGX_HTTP_LOC_CONF,
+    NGX_HTTP_LOC_CONF_OFFSET, NGX_HTTP_MODULE,
 };
 use ngx::http::{self, HTTPModule, MergeConfigError};
 use ngx::{http_request_handler, ngx_log_debug_http, ngx_string};
@@ -92,17 +92,13 @@ impl http::Merge for ModuleConfig {
 unsafe extern "C" fn check_async_work_done(event: *mut ngx_event_t) {
     let ctx = ngx::ngx_container_of!(event, RequestCTX, event);
     let c: *mut ngx_connection_t = (*event).data.cast();
-    let r: *mut ngx_http_request_t = (*c).data.cast();
 
     if (*ctx).done.load(Ordering::Relaxed) {
-        let main = &mut *(*r).main;
-        main.set_count(main.count() - 1);
-        ngx_http_core_run_phases(r);
+        // Triggering async_access_handler again
+        ngx_post_event((*c).write, addr_of_mut!(ngx_posted_events));
     } else {
-        // this doesn't have have good performance but works as a simple thread-safe example and doesn't causes
-        // segfault. The best method that provides both thread-safety and performance requires
-        // an nginx patch.
-        ngx_post_event(event, addr_of_mut!(ngx_posted_next_events));
+        // Checking again after 100ms to avoid busy loop
+        ngx_add_timer(event, 100);
     }
 }
 
@@ -162,10 +158,9 @@ http_request_handler!(async_access_handler, |request: &mut http::Request| {
     ctx.event.handler = Some(check_async_work_done);
     ctx.event.data = request.connection().cast();
     ctx.event.log = unsafe { (*request.connection()).log };
-    unsafe { ngx_post_event(&mut ctx.event, addr_of_mut!(ngx_posted_next_events)) };
-
-    let main = unsafe { &mut *request.as_ref().main };
-    main.set_count(main.count() + 1);
+    unsafe {
+        ngx_add_timer(&mut ctx.event, 100);
+    }
 
     // Request is no longer needed and can be converted to something movable to the async block
     let req = AtomicPtr::new(request.into());
diff --git a/examples/t/async.t b/examples/t/async.t
index 294f551a..98505fdb 100644
--- a/examples/t/async.t
+++ b/examples/t/async.t
@@ -51,6 +51,6 @@ $t->run();
 
 ###############################################################################
 
-like(http_get('/', sleep => 2.1), qr/X-Async-Time:/, 'async handler');
+like(http_get('/index.html'), qr/X-Async-Time:/, 'async handler');
 
 ###############################################################################