Release version v0.5.0 + add --hf-token, use hf-mem as lib, etc.

[alvarobartt]

Description

This PR sets the version to v0.5.0 by running uv version 0.5.0 prior the release; and also includes hf-mem as a lib rather than only as a CLI, adds the --hf-token argument (closes #37, or at least makes it more explicit), and last but not least, uses Claude Sonnet 4.6 via pi to refactor the codebase in an opinionated way (+ some manual intervention) due to the recent community contributions.

Additionally, this PR moves out the KV cache estimation, and applies the feedback mentioned in https://huggingface.co/Qwen/Qwen3.5-397B-A17B/discussions/20#69a5bf82a2b3b0f27e8eacef to handle properly the full and sliding attention, rather than always assuming full attention + use the head_dim if specified instead of calculating it; all the kudos here go to https://huggingface.co/YouJiacheng.

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• I have read and followed the guidelines in CONTRIBUTING.md.
• This has been discussed over an issue or discussion.