threadshare: Port to polling 3.0.0

error[E0277]: the trait bound `i32: AsFd` is not satisfied
   --> generic/threadshare/src/runtime/executor/reactor.rs:248:28
    |
248 |         self.poller.delete(source.raw)
    |                     ------ ^^^^^^^^^^ the trait `AsFd` is not implemented for `i32`
    |                     |
    |                     required by a bound introduced by this call
    |
    = help: the following other types implement trait `AsFd`:
              Poller
              socket2::Socket
              polling::epoll::Poller
              Box<T>
              std::fs::File
              Stdin
              StdinLock<'a>
              Stdout
            and 24 others
    = note: required for `i32` to implement `AsSource`
note: required by a bound in `Poller::delete`
   --> /home/slomo/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polling-3.0.0/src/lib.rs:613:39
    |
613 |     pub fn delete(&self, source: impl AsSource) -> io::Result<()> {
    |                                       ^^^^^^^^ required by this bound in `Poller::delete`

error[E0308]: mismatched types
   --> generic/threadshare/src/runtime/executor/reactor.rs:395:42
    |
395 |         let res = match self.poller.wait(&mut self.events, Some(Duration::ZERO)) {
    |                                     ---- ^^^^^^^^^^^^^^^^ expected `&mut Events`, found `&mut Vec<Event>`
    |                                     |
    |                                     arguments to this method are incorrect
    |
    = note: expected mutable reference `&mut Events`
               found mutable reference `&mut Vec<polling::Event>`
note: method defined here
   --> /home/slomo/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polling-3.0.0/src/lib.rs:656:12
    |
656 |     pub fn wait(&self, events: &mut Events, timeout: Option<Duration>) -> io::Result<usize> {
    |            ^^^^

error[E0277]: the trait bound `i32: AsFd` is not satisfied
   --> generic/threadshare/src/runtime/executor/reactor.rs:418:33
    |
417 | ...                   self.poller.modify(
    |                                   ------ required by a bound introduced by this call
418 | ...                       source.raw,
    |                           ^^^^^^^^^^ the trait `AsFd` is not implemented for `i32`
    |
    = help: the following other types implement trait `AsFd`:
              Poller
              socket2::Socket
              polling::epoll::Poller
              Box<T>
              std::fs::File
              Stdin
              StdinLock<'a>
              Stdout
            and 24 others
    = note: required for `i32` to implement `AsSource`
note: required by a bound in `Poller::modify`
   --> /home/slomo/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polling-3.0.0/src/lib.rs:559:39
    |
559 |     pub fn modify(&self, source: impl AsSource, interest: Event) -> io::Result<()> {
    |                                       ^^^^^^^^ required by this bound in `Poller::modify`

error: cannot construct `polling::Event` with struct literal syntax due to private fields
   --> generic/threadshare/src/runtime/executor/reactor.rs:419:33
    |
419 | ...                   Event {
    |                       ^^^^^
    |
    = note: ... and other private field `extra` that was not provided

error[E0277]: the trait bound `i32: AsFd` is not satisfied
   --> generic/threadshare/src/runtime/executor/reactor.rs:594:21
    |
593 |                 reactor.poller.modify(
    |                                ------ required by a bound introduced by this call
594 |                     self.raw,
    |                     ^^^^^^^^ the trait `AsFd` is not implemented for `i32`
    |
    = help: the following other types implement trait `AsFd`:
              Poller
              socket2::Socket
              polling::epoll::Poller
              Box<T>
              std::fs::File
              Stdin
              StdinLock<'a>
              Stdout
            and 24 others
    = note: required for `i32` to implement `AsSource`
note: required by a bound in `Poller::modify`
   --> /home/slomo/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polling-3.0.0/src/lib.rs:559:39
    |
559 |     pub fn modify(&self, source: impl AsSource, interest: Event) -> io::Result<()> {
    |                                       ^^^^^^^^ required by this bound in `Poller::modify`

error: cannot construct `polling::Event` with struct literal syntax due to private fields
   --> generic/threadshare/src/runtime/executor/reactor.rs:595:21
    |
595 |                     Event {
    |                     ^^^^^
    |
    = note: ... and other private field `extra` that was not provided

error[E0277]: the trait bound `i32: AsFd` is not satisfied
   --> generic/threadshare/src/runtime/executor/reactor.rs:784:21
    |
783 |                 reactor.poller.modify(
    |                                ------ required by a bound introduced by this call
784 |                     handle.borrow().source.raw,
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsFd` is not implemented for `i32`
    |
    = help: the following other types implement trait `AsFd`:
              Poller
              socket2::Socket
              polling::epoll::Poller
              Box<T>
              std::fs::File
              Stdin
              StdinLock<'a>
              Stdout
            and 24 others
    = note: required for `i32` to implement `AsSource`
note: required by a bound in `Poller::modify`
   --> /home/slomo/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polling-3.0.0/src/lib.rs:559:39
    |
559 |     pub fn modify(&self, source: impl AsSource, interest: Event) -> io::Result<()> {
    |                                       ^^^^^^^^ required by this bound in `Poller::modify`

error: cannot construct `polling::Event` with struct literal syntax due to private fields
   --> generic/threadshare/src/runtime/executor/reactor.rs:785:21
    |
785 |                     Event {
    |                     ^^^^^
    |
    = note: ... and other private field `extra` that was not provided

Needs a bit of actual work, I think the main change here is the switch to the safe file descriptor APIs.

CC @fengalin