rebaseInner

    fn rebaseInner(w: *Writer, preserve: usize, capacity: usize, eos: bool) Writer.Error!void {
        const h: *Huffman = @fieldParentPtr("writer", w);
        assert(preserve + capacity <= w.buffer.len);
        if (eos) assert(capacity == w.buffer.len);

        const preserved = @min(w.end, preserve);
        var remaining = w.buffer[0 .. w.end - preserved];
        while (remaining.len > max_tokens) { // not >= so there is always a block down below
            const bytes = remaining[0..max_tokens];
            remaining = remaining[max_tokens..];
            try h.outputBytes(bytes, false);
        }

        // eos check required for empty block
        if (w.buffer.len - (remaining.len + preserved) < capacity or eos) {
            const bytes = remaining;
            remaining = &.{};
            try h.outputBytes(bytes, eos);
        }

        _ = w.consume(w.end - preserved - remaining.len);
    }