[firefox][unity] Add support for cumulative updates and use it in a few scripts (#295)

Generic support for cumulative updates has been added to speed up execution time of some scripts that were very long (in comparison with the vast majority of products), usually because they were involving a lot of HTTP requests.

This feature was developed particularily for the firefox.py and unity.py scripts, which was often very long to execute (a minute or moreaccording to GHA summaries). Those scripts has been updated to make use of this new feature.

src/unity.py

@@ -1,25 +1,27 @@
 from bs4 import BeautifulSoup
 from common import dates, http, releasedata
 
-# Fetches the Unity LTS releases from the Unity website. Non-LTS releases are not listed there,
-# so this automation is only partial.
-#
-# This script iterates over all pages of the Unity LTS releases page, which is paginated.
-# It keeps fetching the next page until there is no next page link.
+"""Fetches the Unity LTS releases from the Unity website. Non-LTS releases are not listed there, so this automation
+is only partial.
 
-BASE_URL = "https://unity.com/releases/editor/qa/lts-releases"
+This script is cumulative, only the first page is fetched (e.g. the first ten versions). This is because:
+- it is too long to fetch all (at least 30s, usually more than a minute),
+- this generates too many requests to the unity.com servers,
+- fetching multiple pages in parallel is raising a lot of errors and makes the overall process slower (this was tested
+  during https://github.com/endoflife-date/release-data/pull/194),
+- and anyway oldest versions are never updated.
 
-next_page_url = BASE_URL
-with releasedata.ProductData("unity") as product_data:
-    # Do not try to fetch multiple pages in parallel: it is raising a lot of errors and make the overall process slower.
-    while next_page_url:
-        response = http.fetch_url(next_page_url)
-        soup = BeautifulSoup(response.text, features="html5lib")
+Note that it was assumed that:
+- the script is ran regularly enough to keep the versions up to date (once a day or week looks enough),
+- there is never more than 10 new LTS versions at a time.
 
-        for release in soup.find_all('div', class_='component-releases-item__show__inner-header'):
-            version = release.find('h4').find('span').text
-            date = dates.parse_datetime(release.find('time').attrs['datetime'])
-            product_data.declare_version(version, date)
+The script will need to be updated if someday those conditions are not met."""
 
-        next_link = soup.find('a', {"rel": "next"})
-        next_page_url = BASE_URL + next_link.attrs['href'] if next_link else None
+with releasedata.ProductData("unity", cumulative_update=True) as product_data:
+    response = http.fetch_url("https://unity.com/releases/editor/qa/lts-releases")
+    soup = BeautifulSoup(response.text, features="html5lib")
+
+    for release in soup.find_all('div', class_='component-releases-item__show__inner-header'):
+        version = release.find('h4').find('span').text
+        date = dates.parse_datetime(release.find('time').attrs['datetime'])
+        product_data.declare_version(version, date)