### Description

When completing a zero_shot classification task, there is the input sequence (provided by the user), and labels (also provided by the user). 

Tokenization as it is done now tokenizes the input sequence len(labels) times. We should really only do it once and pass those tokenized values to request builder. 

Some of the changes introduce here: https://github.com/elastic/elasticsearch/pull/84777 should make implementing this simpler (as there will be a unified temporary tokenization result object).
x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/BertTokenizer.java
throw new UncheckedIOException(ex);
        }
        return new InnerTokenization(new ArrayList<>(wordPieceAnalyzer.getTokens()), tokenPositionMap);
    }
    @Override
    public void close() {
        wordPieceAnalyzer.close();
    }
    public int getMaxSequenceLength() {
        return maxSequenceLength;
    }
    public static Builder builder(List<String> vocab, Tokenization tokenization) {
        return new Builder(vocab, tokenization);
    }
    public static class Builder {
        protected final List<String> originalVocab;
        protected final SortedMap<String, Integer> vocab;
        protected boolean doLowerCase;
        protected boolean doTokenizeCjKChars = true;
        protected boolean withSpecialTokens;
        protected int span = -1;
        protected int maxSequenceLength;
        protected Boolean doStripAccents = null;
        protected Set<String> neverSplit;
        protected Builder(List<String> vocab, Tokenization tokenization) {
            this.originalVocab = vocab;
            this.vocab = buildSortedVocab(vocab);
            this.doLowerCase = tokenization.doLowerCase();
            this.withSpecialTokens = tokenization.withSpecialTokens();
            this.maxSequenceLength = tokenization.maxSequenceLength();