ref(ratelimiter): Simplify exception handling flow

Move success return inside try block and remove finally/condition.
The error return is now reached only when an exception occurs.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: phacops

snuba/state/rate_limit.py

@@ -259,8 +259,6 @@ def rate_limit_start_request(
                 bucket = _get_bucket_key(rate_limit_prefix, rate_limit_params.bucket, shard_i)
                 pipe.zcount(bucket, "({:f}".format(now), "+inf")
 
-        historical = -1
-        concurrent = -1
         try:
             results = pipe.execute()
             pipe_results = iter(results)
@@ -279,6 +277,9 @@ def rate_limit_start_request(
                 concurrent = sum(next(pipe_results) for _ in range(rate_limit_shard_factor))
             else:
                 concurrent = 0
+
+            per_second = historical / float(state.rate_lookback_s)
+            return RateLimitStats(rate=per_second, concurrent=concurrent)
         except RedisTimeoutError:
             # Emit metric for timeout, but don't log since this is expected
             # when Redis is slow. We fail open to avoid blocking requests.
@@ -287,14 +288,9 @@ def rate_limit_start_request(
             # if something goes wrong, we don't want to block the request,
             # set the values such that they pass under any limit
             logger.exception(ex)
-        finally:
-            if historical == -1:
-                return RateLimitStats(rate=-1, concurrent=-1)
-
-    per_second = historical / float(state.rate_lookback_s)
 
-    stats = RateLimitStats(rate=per_second, concurrent=concurrent)
-    return stats
+    # Return fail-open stats if an exception occurred
+    return RateLimitStats(rate=-1, concurrent=-1)
 
 
 def rate_limit_finish_request(