Robot Framework Allure listener generates a huge amount of files

**Describe the bug**
When I use the Allure listener with Robot-Framework, a huge amount of files are generated.
For example : around 3000 json & html files (13MB !) are generated for a couple of basics Robot-Framework tests.
The final Allure report generated from the same tests also contains around 1500 files (6MB).

This situation has a limited impact for some basics tests, but, in case of my real tests campaign, more than 800.000 files are generated, for more than 1GB size ! This lead to memory issues or disk spaces failures.

**To Reproduce**
Steps to reproduce the behavior:
1. Start a basic Robot-Framework test campaign with the Allure listener ( --listener "allure_robotframework;allure-export"
2. Check the number of files in the "allure-export" folder and its size.
3. Generate the Allure report from the previous export files.
4. Check the number of files in the report folder, and its size .

**Expected behavior**
The listener output and Allure report should be optimized to reduce number of files generated and their size.

**Environment (please complete the following information):**

Allure version: 2.12.1
Test framework: robotframework@3.0.2
Allure adaptor: allure-robotframework@2.8.6

まず、指定された Robot Framework listener command で問題を再現し、allure-export フォルダーと generated report フォルダーを調べて、ファイル数とサイズを比較します。payload にはソースファイルやテストの名前がないため、その再現結果から listener と report-generation のエントリーポイントを追跡します。完了の条件は、レポートの内容を失わずにファイル数と出力サイズが大幅に減ることです。

索引モデルが issue の本文から書いたものです。