A WasiEnv now has a flag that signifies if it's allowed
to block the current thread and the flag is expected to
be referenced when the current thread can be blocked for
optimising the performance. In addition, the flag is set
true when wasm modules are invoked via the CLI. wasmer-wasix
uses a tokio runtime for many things according to wasmerio#4299, but
tokio does not always bring the best performance in Wasmer
as described in wasmerio#4738, hence this update.

Signed-off-by: Daichi Fukui <daichi1.fukui@toshiba.co.jp>

Allow different sleep form of poll_oneoff, which
just sleeps for relative time using std::thread::sleep.
That form of poll_oneoff is only available if there is
only one subscription and it is allowed to block
the current thread, contributing to more consistent
sleep times. This update would help improve
the real-time performance of wasmer.

Closes: wasmerio#4738

Signed-off-by: Daichi Fukui <daichi1.fukui@toshiba.co.jp>