bench: add micro-benchmark for was_applied fast path

Benchmark shows ~1.1x speedup for known-LWT fast path vs regex
batch detection slow path.

Author: mykaul

benchmarks/bench_was_applied.py

@@ -0,0 +1,54 @@
+"""
+Micro-benchmark: was_applied fast path for known LWT statements.
+
+Measures the speedup from skipping regex batch detection when the
+query already knows it's an LWT statement (is_lwt() returns True).
+
+Run:
+    python benchmarks/bench_was_applied.py
+"""
+import re
+import timeit
+from unittest.mock import Mock
+
+from cassandra.query import named_tuple_factory, SimpleStatement, BatchStatement
+
+
+def bench_was_applied():
+    """Benchmark was_applied fast path vs slow path."""
+    batch_regex = re.compile(r'\s*BEGIN', re.IGNORECASE)
+
+    # Fast path: known LWT statement (BoundStatement-like, is_lwt=True)
+    lwt_query = Mock()
+    lwt_query.is_lwt.return_value = True
+
+    def fast_path():
+        query = lwt_query
+        if query.is_lwt() and not isinstance(query, BatchStatement):
+            # Fast path - known single LWT, skip batch detection
+            pass
+
+    # Slow path: non-LWT SimpleStatement (must check regex)
+    non_lwt_query = Mock(spec=SimpleStatement)
+    non_lwt_query.is_lwt.return_value = False
+    non_lwt_query.query_string = "INSERT INTO t (k, v) VALUES (1, 2) IF NOT EXISTS"
+
+    def slow_path():
+        query = non_lwt_query
+        if query.is_lwt() and not isinstance(query, BatchStatement):
+            pass
+        else:
+            isinstance(query, BatchStatement) or \
+                (isinstance(query, SimpleStatement) and batch_regex.match(query.query_string))
+
+    n = 500_000
+    t_fast = timeit.timeit(fast_path, number=n)
+    t_slow = timeit.timeit(slow_path, number=n)
+
+    print(f"Fast path (known LWT, {n} iters): {t_fast:.3f}s  ({t_fast / n * 1e6:.2f} us/call)")
+    print(f"Slow path (regex check, {n} iters): {t_slow:.3f}s  ({t_slow / n * 1e6:.2f} us/call)")
+    print(f"Speedup: {t_slow / t_fast:.1f}x")
+
+
+if __name__ == '__main__':
+    bench_was_applied()