Replace Eventfd with EventNotifier/EventConsumer

[uran0sH]

Summary of the PR

Eventfd is Linux-specific. To support more platforms, we replace it with
the EventNotifier/EventConsumer abstractions.
EventSender and EventReceiver are wrappers that encapsulate eventfd functionality
Use pipefd to replace eventfd in the test.

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• [ x ] All commits in this PR have Signed-Off-By trailers (with
  git commit -s), and the commit message has max 60 characters for the
  summary and max 75 characters for each description line.
• [ x ] All added/changed functionality has a corresponding unit/integration
  test.
• [ x ] All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• [ x ] Any newly added unsafe code is properly documented.

[uran0sH]

cc @stefano-garzarella @germag @osteffenrh

[stefano-garzarella]

@uran0sH marked as draft, since we need a new vmm-sys-util release before merging this.

[stefano-garzarella]

@uran0sH please rebase and check CI (come failures need the new rust version we are updating in the CI, but others are related to format, etc.)

[stefano-garzarella]

@uran0sH we just merged #309 so you should be able to use the new API requiring 1.87

[stefano-garzarella]

@uran0sH please check the CI, there some clippy warning to fix, but also some tests blocked for more than 60s. Should I restart the CI or it's an issue we need to fix?

[uran0sH]

@uran0sH please check the CI, there some clippy warning to fix, but also some tests blocked for more than 60s. Should I restart the CI or it's an issue we need to fix?

I think it's an issue

[uran0sH]

@uran0sH please check the CI, there some clippy warning to fix, but also some tests blocked for more than 60s. Should I restart the CI or it's an issue we need to fix?

I think it's an issue

Fix this issue by changing this line to into_raw_fd() (https://github.com/rust-vmm/vhost/pull/308/files#diff-e1c9dc7802234bc118de8314ec9cacc98066eea325a6f14ff5887ece3466d5a3R96). Because when we use pipe, using as_raw_fd will cause the consumer's fd to be closed, like this (https://github.com/rust-vmm/vhost/pull/308/files#diff-c9eba2d5821720c1f7e164d0d01d85b14040d8f3200fac89607fdd1af09d5491R111). So we need to take the ownership of this fd.