fix: handle missing content-length header in _get_tokenizer_config_size

When a server uses chunked transfer encoding, neither content-length nor
x-goog-stored-content-length headers are present, leaving size as None.
The subsequent int() cast then raises a TypeError.

Add an explicit None check that raises a ValueError instead, which is
caught gracefully by the existing try/except in both callers (get_hf_tokenizer
and async_get_hf_tokenizer) — tokenizer download proceeds normally.

Fixes: #762

Author: fern-support

src/cohere/manually_maintained/tokenizers.py

@@ -99,4 +99,6 @@ def _get_tokenizer_config_size(tokenizer_url: str) -> float:
         if size:
             break
 
-    return round(int(typing.cast(int, size)) / 1024 / 1024, 2)
+    if size is None:
+        raise ValueError("No content-length header found (server may use chunked transfer encoding)")
+    return round(int(size) / 1024 / 1024, 2)