hdrs async open can cause memory leak

[fMeow]

Change async_open back to open massively reduce memory usage. Invesigating.

• updated (2024.03.23)
  Setting log level to TRACE, I foundhdrs::File instances correctly dropped. And I tried offload hdrs file reading operation to avoid blocking on async runtime via tokio::task::spawn_blocking and it works like a charm. So it is highly possible that the underlying blocking mechanism currently at use is at fault.

[Xuanwo]

Maybe related to blocking::Unblock?

[fMeow]

Agree, though I don't have evidence. Maybe Unblock does not correctly free memories of data that passed back to original async runtime?