feat: disallow ModuleRunnerTransport to be async

[sapphi-red]

Description

Alternative to #18750.

Instead of making import.meta.hot.send async, this PR makes ModuleRunnerTransport to disallow send to be async. This way we can avoid the breaking change.

[sapphi-red]

For sends that were called while connecting the error would be voided and won't be able to catch by the user. In Vite 5, the error happened for the send call later that was called (which is confusing I guess).

vite/packages/vite/src/shared/hmr.ts

Lines 180 to 190 in c54c860

	public send(message: string): void {
	this.queue.push(message)
	this.flush()
	}
	public flush(): void {
	if (this.connection.isReady()) {
	this.queue.forEach((msg) => this.connection.send(msg))
	this.queue = []
	}
	}

[sapphi-red]

closing as #18753 was merged