[internal] refacto tests for inference snippets

[Wauplin]

This PR does nothing else than updating packages/tasks-gen/scripts/generate-snippets-fixtures.ts which is an internal script used to test the inference snippets. Goal of this PR is to store generated snippet under a new file structure like this:

./snippets-fixtures/automatic-speech-recognition/python/huggingface_hub/1.hf-inference.py

instead of

./snippets-fixtures/automatic-speech-recognition/1.huggingface_hub.hf-inference.py

In practice the previous file naming was annoying as it meant that adding a new snippet in a client type could lead to renaming another file (due to the 0., 1., ... prefixes).

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Typically in #1273 it makes the PR much bigger by e.g. deleting 1.openai.hf-inference.py and creating 2.openai.hf-inference.py just because a new 1.requests.hf-inference.py has been added.

Separating files by language + client avoid these unnecessary problems.

[Wauplin]

Merging as it's a purely internal change that could make #1273 and next PRs easier to review.