py : convert-hf-to-gguf-update improvements (#7340)

* convert-hf-to-gguf-update: automate updating

* convert-hf-to-gguf-update: improve download

* share requests session for performance
* create directories only when needed, don't skip downloads when empty directory encountered
* be more graceful about errors

convert-hf-to-gguf.py

@@ -402,6 +402,7 @@ class Model:
     # NOTE: this function is generated by convert-hf-to-gguf-update.py
     #       do not modify it manually!
     # ref:  https://github.com/ggerganov/llama.cpp/pull/6920
+    # Marker: Start get_vocab_base_pre
     def get_vocab_base_pre(self, tokenizer) -> str:
         # encoding this string and hashing the resulting tokens would (hopefully) give us a unique identifier that
         # is specific for the BPE pre-tokenizer used by the model
@@ -489,6 +490,7 @@ class Model:
         logger.debug(f"chkhsh: {chkhsh}")
 
         return res
+        # Marker: End get_vocab_base_pre
 
     def _set_vocab_gpt2(self) -> None:
         tokens, toktypes, tokpre = self.get_vocab_base()