Migrate Unity scraper to use Editor Release API (#558)

Switch from HTML scraping to the official Unity Editor Release API.

- Fetch versions from paginated API endpoint
- Filter out ALPHA and BETA stream releases
- Process all available versions (not just first page)

Closes https://github.com/endoflife-date/endoflife.date/issues/9418.

src/unity.py

@@ -1,27 +1,37 @@
 from common import dates, http
 from common.releasedata import ProductData, config_from_argv
 
-"""Fetches the Unity LTS releases from the Unity website. Non-LTS releases are not listed there, so this automation
-is only partial.
+"""Fetches Unity versions from the Unity Editor Release API.
 
-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.
-
-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.
-
-The script will need to be updated if someday those conditions are not met."""
+This script fetches stable releases from the Unity API, filtering out alpha, beta, and other pre-release versions.
+The API provides paginated results with all Unity versions across different streams (TECH, LTS, BETA, ALPHA).
+"""
 
 config = config_from_argv()
 with ProductData(config.product) as product_data:
-    html = http.fetch_html(config.url)
+    offset = 0
+    limit = 25
 
-    for release in html.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)
+    while True:
+        url = f"{config.url}?limit={limit}&offset={offset}"
+        data = http.fetch_json(url)
+
+        if 'results' not in data:
+            break
+
+        for release in data['results']:
+            version = release['version']
+
+            # Skip pre-release versions (ALPHA, BETA, etc.)
+            stream = release.get('stream', '')
+            if stream in ('ALPHA', 'BETA'):
+                continue
+
+            date = dates.parse_datetime(release['releaseDate'])
+            product_data.declare_version(version, date)
+
+        # Check if we've reached the end
+        total = data.get('total', 0)
+        offset += limit
+        if offset >= total:
+            break