use try_send to replace send.await, unbounded channel should always b… (bevyengine#7745)

…e sendable, this improves performance

# Objective

- From prev experience, `.await` is not free, also I did a profiling a half year ago, bevy's multithread executor spend lots cycles on ArcWaker.

## Solution

-  this pr replace `sender.send().await` to `sender.try_send()` to cut some future/await cost.

benchmarked on `empty system`
```bash
➜ critcmp send_base send_optimize
group                                         send_base                              send_optimize
-----                                         ---------                              -------------
empty_systems/000_systems                     1.01      2.8±0.03ns        ? ?/sec    1.00      2.8±0.02ns        ? ?/sec
empty_systems/001_systems                     1.00      5.9±0.21µs        ? ?/sec    1.01      5.9±0.23µs        ? ?/sec
empty_systems/002_systems                     1.03      6.4±0.26µs        ? ?/sec    1.00      6.2±0.19µs        ? ?/sec
empty_systems/003_systems                     1.01      6.5±0.17µs        ? ?/sec    1.00      6.4±0.20µs        ? ?/sec
empty_systems/004_systems                     1.03      7.0±0.24µs        ? ?/sec    1.00      6.8±0.18µs        ? ?/sec
empty_systems/005_systems                     1.04      7.4±0.35µs        ? ?/sec    1.00      7.2±0.21µs        ? ?/sec
empty_systems/010_systems                     1.00      9.0±0.28µs        ? ?/sec    1.00      9.1±0.80µs        ? ?/sec
empty_systems/015_systems                     1.01     10.9±0.36µs        ? ?/sec    1.00     10.8±1.29µs        ? ?/sec
empty_systems/020_systems                     1.12     12.7±0.67µs        ? ?/sec    1.00     11.3±0.37µs        ? ?/sec
empty_systems/025_systems                     1.12     14.6±0.39µs        ? ?/sec    1.00     13.0±1.02µs        ? ?/sec
empty_systems/030_systems                     1.12     16.2±0.39µs        ? ?/sec    1.00     14.4±0.37µs        ? ?/sec
empty_systems/035_systems                     1.19     18.2±0.97µs        ? ?/sec    1.00     15.3±0.48µs        ? ?/sec
empty_systems/040_systems                     1.12     20.6±0.58µs        ? ?/sec    1.00     18.3±1.87µs        ? ?/sec
empty_systems/045_systems                     1.18     22.7±0.57µs        ? ?/sec    1.00     19.2±0.46µs        ? ?/sec
empty_systems/050_systems                     1.03     21.9±0.92µs        ? ?/sec    1.00     21.3±0.96µs        ? ?/sec
empty_systems/055_systems                     1.13     25.7±1.00µs        ? ?/sec    1.00     22.8±0.50µs        ? ?/sec
empty_systems/060_systems                     1.35     30.0±2.57µs        ? ?/sec    1.00     22.2±1.04µs        ? ?/sec
empty_systems/065_systems                     1.28     31.7±0.76µs        ? ?/sec    1.00     24.8±0.79µs        ? ?/sec
empty_systems/070_systems                     1.33    36.8±10.37µs        ? ?/sec    1.00     27.6±0.55µs        ? ?/sec
empty_systems/075_systems                     1.25     38.0±0.83µs        ? ?/sec    1.00     30.3±0.63µs        ? ?/sec
empty_systems/080_systems                     1.33     41.7±1.22µs        ? ?/sec    1.00     31.4±1.01µs        ? ?/sec
empty_systems/085_systems                     1.27     45.6±2.54µs        ? ?/sec    1.00     35.8±4.06µs        ? ?/sec
empty_systems/090_systems                     1.29     48.3±5.33µs        ? ?/sec    1.00     37.6±5.32µs        ? ?/sec
empty_systems/095_systems                     1.16     45.7±0.97µs        ? ?/sec    1.00     39.4±2.75µs        ? ?/sec
empty_systems/100_systems                     1.14     49.5±4.26µs        ? ?/sec    1.00     43.5±1.06µs        ? ?/sec
```

Author: shuoli84

crates/bevy_ecs/src/schedule/executor/multi_threaded.rs

@@ -451,8 +451,7 @@ impl MultiThreadedExecutor {
                 sender.close();
             } else {
                 sender
-                    .send(system_index)
-                    .await
+                    .try_send(system_index)
                     .unwrap_or_else(|error| unreachable!("{}", error));
             }
         };
@@ -508,8 +507,7 @@ impl MultiThreadedExecutor {
                     sender.close();
                 } else {
                     sender
-                        .send(system_index)
-                        .await
+                        .try_send(system_index)
                         .unwrap_or_else(|error| unreachable!("{}", error));
                 }
             };
@@ -532,8 +530,7 @@ impl MultiThreadedExecutor {
                     sender.close();
                 } else {
                     sender
-                        .send(system_index)
-                        .await
+                        .try_send(system_index)
                         .unwrap_or_else(|error| unreachable!("{}", error));
                 }
             };