Implement proper AsyncSeek+AsyncReader

We should really fix this issue in order to not download excessive bytes for the get_content() method. Potentially have those changes more upstream so that all storage backends can benefit from the improvement:

htsget-rs/htsget-search/src/storage/aws.rs

Lines 147 to 151 in 40a9c93

    
           async fn get_content<K: AsRef<str> + Send>(&self, key: K, options: GetOptions) -> Result<Bytes> { 
        
             // It would be nice to use a ready-made type with a ByteStream that implements AsyncRead + AsyncSeek 
        
             // in order to avoid reading the whole byte buffer into memory. A custom type could be made similar to 
        
             // https://users.rust-lang.org/t/what-to-pin-when-implementing-asyncread/63019/2 which could be based off 
        
             // StreamReader.

Otherwise the side effects are unnecessary egress charges for cloud and prohibitively slow requests/responses.

	async fn get_content<K: AsRef<str> + Send>(&self, key: K, options: GetOptions) -> Result<Bytes> {
	// It would be nice to use a ready-made type with a ByteStream that implements AsyncRead + AsyncSeek
	// in order to avoid reading the whole byte buffer into memory. A custom type could be made similar to
	// https://users.rust-lang.org/t/what-to-pin-when-implementing-asyncread/63019/2 which could be based off
	// StreamReader.