requirements : update transformers/torch for Embedding Gemma (#15828)

* requirements : update transformers/torch for Embedding Gemma

This commit updates the requirements to support converting
Embedding Gemma 300m models.

The motivation for this change is that during development I had a local
copy of the transformers package which is what I used for converting
the models. This was a mistake on my part and I should have also updated
my transformers version to the official release.

I had checked the requirements/requirements-convert_legacy_llama.txt
file and noted that the version was >=4.45.1,<5.0.0 and came to the
conculusion that no updated would be needed, this assumed that
Embedding Gemma would be in a transformers release at the time
Commit fb15d649ed ("llama : add support
for EmbeddingGemma 300m (#15798)) was merged. So anyone wanting to
convert themselves would be able to do so. However, Embedding Gemma is
a preview release and this commit updates the requirements to use this
preview release.

* resolve additional python dependencies

* fix pyright errors in tokenizer test and remove unused import

requirements/requirements-convert_hf_to_gguf.txt

@@ -2,7 +2,9 @@ mistral-common>=1.8.3
 
 -r ./requirements-convert_legacy_llama.txt
 --extra-index-url https://download.pytorch.org/whl/cpu
-torch~=2.4.0; platform_machine != "s390x"
+
+## Embedding Gemma requires PyTorch 2.6.0 or later
+torch~=2.6.0; platform_machine != "s390x"
 
 # torch s390x packages can only be found from nightly builds
 --extra-index-url https://download.pytorch.org/whl/nightly