refactor: convert fetchPartCallback class from java to kotlin

package com.fsck.k9.mail.store.imap;

import java.io.IOException;

import com.fsck.k9.mail.BodyFactory;

import com.fsck.k9.mail.Part;

import com.fsck.k9.mail.filter.FixedLengthInputStream;

import com.fsck.k9.mail.internet.MimeHeader;

class FetchPartCallback implements ImapResponseCallback {

    private final Part part;

    private final BodyFactory bodyFactory;

    FetchPartCallback(Part part, BodyFactory bodyFactory) {

        this.part = part;

        this.bodyFactory = bodyFactory;

    }

    @Override

    public Object foundLiteral(ImapResponse response, FixedLengthInputStream literal) throws IOException {

        if (response.getTag() == null && ImapResponseParser.equalsIgnoreCase(response.get(1), "FETCH")) {

package com.fsck.k9.mail.store.imap

import com.fsck.k9.mail.BodyFactory

import com.fsck.k9.mail.Part

import com.fsck.k9.mail.filter.FixedLengthInputStream

import com.fsck.k9.mail.internet.MimeHeader

import java.io.IOException

internal class FetchPartCallback(private val part: Part, private val bodyFactory: BodyFactory) :

    ImapResponseCallback {

    @Throws(IOException::class)

    override fun foundLiteral(response: ImapResponse, literal: FixedLengthInputStream): Any? {

        if (response.tag == null && ImapResponseParser.equalsIgnoreCase(response[1], "FETCH")) {

            // TODO: check for correct UID

            String contentTransferEncoding = part.getHeader(MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING)[0];

            String contentType = part.getHeader(MimeHeader.HEADER_CONTENT_TYPE)[0];

            val contentTransferEncoding = part.getHeader(MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING)[0]

            val contentType = part.getHeader(MimeHeader.HEADER_CONTENT_TYPE)[0]

            return bodyFactory.createBody(contentTransferEncoding, contentType, literal);

            return bodyFactory.createBody(contentTransferEncoding, contentType, literal)

        }

        return null;

        return null

    }

}