fix(proxy): skip URLs without scheme in load_proxy_tiers()

Validates each URL in PROXY_URLS_DATACENTER / PROXY_URLS_RESIDENTIAL:
logs a warning and skips any entry missing an http:// or https:// scheme
instead of passing malformed URLs that cause SSL or connection errors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

extract/padelnomics_extract/src/padelnomics_extract/proxy.py

@@ -88,8 +88,14 @@ def load_proxy_tiers() -> list[list[str]]:
     for var in ("PROXY_URLS_DATACENTER", "PROXY_URLS_RESIDENTIAL"):
         raw = os.environ.get(var, "")
         urls = [u.strip() for u in raw.split(",") if u.strip()]
-        if urls:
-            tiers.append(urls)
+        valid = []
+        for url in urls:
+            if not url.startswith(("http://", "https://")):
+                logger.warning("%s contains URL without scheme, skipping: %s", var, url[:60])
+                continue
+            valid.append(url)
+        if valid:
+            tiers.append(valid)
 
     return tiers