logreader.py: concurrent file existence checks (#34875)

* concurrent file existence checks

* upper bound on parallel queries

---------

Co-authored-by: Shane Smiskol <shane@smiskol.com>

tools/lib/logreader.py

@@ -13,6 +13,7 @@ import warnings
 import zstandard as zstd
 
 from collections.abc import Callable, Iterable, Iterator
+from concurrent.futures import ThreadPoolExecutor, as_completed
 from urllib.parse import parse_qs, urlparse
 
 from cereal import log as capnp_log
@@ -201,9 +202,15 @@ def direct_source(file_or_url: str) -> list[LogPath]:
 
 
 def get_invalid_files(files):
-  for f in files:
-    if f is None or not file_exists(f):
-      yield f
+  if not files:
+    return
+
+  with ThreadPoolExecutor(max_workers=32) as executor:
+    future_to_file = {executor.submit(file_exists, file): file for file in files}
+    for future in as_completed(future_to_file):
+      file = future_to_file[future]
+      if not future.result():
+        yield file
 
 
 def check_source(source: Source, *args) -> list[LogPath]: