Minor refactor: use `impl AsRef<Path>` to make `from_path` more flexible (#419)

//! }

//!

//! async fn bytestream_from_file() -> GetObjectInput {

//!     let f = Path::new("docs/some-large-file.csv");

//!     let bytestream = ByteStream::from_path(&f).await.expect("valid path");

//!     let bytestream = ByteStream::from_path("docs/some-large-file.csv")

//!         .await

//!         .expect("valid path");

//!     GetObjectInput { body: bytestream }

//! }

//! ```

    /// use smithy_http::byte_stream::ByteStream;

    /// use std::path::Path;

    ///  async fn make_bytestream() -> ByteStream {

    ///     ByteStream::from_path(&Path::new("docs/rows.csv")).await.expect("file should be readable")

    ///     ByteStream::from_path("docs/rows.csv").await.expect("file should be readable")

    /// }

    /// ```

    #[cfg(feature = "bytestream-util")]

    #[cfg_attr(docsrs, doc(cfg(feature = "bytestream-util")))]

    pub async fn from_path(path: &Path) -> Result<Self, Error> {

    pub async fn from_path(path: impl AsRef<Path>) -> Result<Self, Error> {

        let path = path.as_ref();

        let path_buf = path.to_path_buf();

        let sz = tokio::fs::metadata(path)

            .await

        for i in 0..10000 {

            writeln!(file, "Brian was here. Briefly. {}", i)?;

        }

        let body = ByteStream::from_path(file.path()).await?.into_inner();

        let body = ByteStream::from_path(&file).await?.into_inner();

        // assert that a valid size hint is immediately ready

        assert_eq!(body.size_hint().exact(), Some(298890));

        let mut body1 = body.try_clone().expect("retryable bodies are cloneable");