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

Inizia riproducendo il problema con il listener command di Robot Framework indicato ed esamina le cartelle allure-export e generated report, confrontando il numero e le dimensioni dei file. Il payload non nomina file sorgente né test, quindi ricostruisci i punti di ingresso di listener e report-generation partendo da quella riproduzione; il lavoro è completato quando ci sono sostanzialmente meno file e un output più piccolo senza perdere contenuto del report.

Scritto dal modello di indicizzazione a partire dal testo della issue.