Update download badges in README.md

[mlejva]

Update broken downloads badge

---

Note

Low Risk
Documentation-only change that updates external badge image URLs and styling; no runtime or build behavior is affected.

Overview
Fixes broken download badges in README.md and packages/python-sdk/README.md.

The PyPI badge is switched from shields.io to a Pepy monthly downloads badge, and the NPM badge label/styling is updated to explicitly show monthly downloads.

^{Written by Cursor Bugbot for commit 811324d. This will update automatically on new commits. Configure here.}

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Latest commit: 811324d

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