v1.1.0

Changes

• Consolidate FileExt and AsyncFileExt into single crate-root traits
  (fs4::FileExt, fs4::AsyncFileExt) instead of generating a distinct
  trait per backend module. The per-backend modules (fs4::tokio,
  fs4::async_std, fs4::smol, fs4::fs_err2, fs4::fs_err3,
  fs4::fs_err2_tokio, fs4::fs_err3_tokio) now re-export the unified
  crate-root trait. Method-call sites that import the trait via use
  continue to compile unchanged; code that named two backend traits as
  distinct types will see them unify.
• Add blanket impls impl<F: FileExt + ?Sized> FileExt for &F and
  impl<F: AsyncFileExt + ?Sized> AsyncFileExt for &F, so the
  extension methods are now callable through shared references.
• Seal FileExt and AsyncFileExt via a private sealed::Sealed
  supertrait, so the set of implementing types is closed to the
  concrete file types fs4 already supports (and references to them).
  This locks in the freedom to add methods to either trait in future
  minor releases without breaking downstream impls.
• Add DynAsyncFileExt, an object-safe mirror of AsyncFileExt whose
  async methods return BoxFuture<'_, T> (alias for
  Pin<Box<dyn Future<Output = T> + Send + '_>>). Use it whenever
  type erasure is needed (Box<dyn DynAsyncFileExt>,
  &dyn DynAsyncFileExt); prefer the static AsyncFileExt for
  generic code since it has no allocation or dynamic-dispatch
  overhead. Every type implementing AsyncFileExt also implements
  DynAsyncFileExt, and the trait is sealed.
• Mark the delegating methods #[inline(always)] (skipped under
  tarpaulin coverage builds).