fix: enable public access to ManifestEntry properties

[a-agmon]

resolves #282 The purpose of the PR is to change the ManifestEntry properties and FileScanTask data_file() method to public in order to enable public access to the file metadata API. Some consumers are interested in the file paths that are part of the current table and their properties for query and monitoring purposes.

[a-agmon]

Just to add to the motivation, part of the purpose here is to allow this kind of API access:

    let mut stream = table_scan.plan_files().await?;
    while let Some(file) = stream.next().await {
        let data_file = file?.data_file();
        println!("---------------------------------");
        println!("File Path: {:?}", data_file.file_path());
        println!("File Size: {:?}", data_file.file_size_in_bytes());
    }

My team is using these APIs to creat a layer of monitoring on top of Iceberg table that can help track issues and identify problems

[a-agmon]

Hi @a-agmon Thanks for this pr. But per our previous discussion, we prefer to expose getter methods rather fields directly to user, you can see the discussion here.

Thanks @liurenjie1024 ! Sure. I will fix this.

[a-agmon]

Hi @liurenjie1024 , @Xuanwo I have addressed the issues and updated the PR. Please let me know what do you think

[liurenjie1024]

cc @Xuanwo Any other comments?