refactor(python)!: rename import package sdk -> quicknode_sdk

[johnpmitsch]

Summary

• Renames the Python import package from the generic sdk to quicknode_sdk. Users now write from quicknode_sdk import QuicknodeSdk.
• The PyPI distribution name (quicknode-sdk) and the Rust core crate name do not change — only the Python import path.
• No backwards-compat shim: still on the 0.1.x line per repo policy, so this is a clean break.

Why

The old import name (sdk) is a footgun for users — it shadows any local sdk/ directory and reads poorly in third-party code. Every other language binding in this repo is namespaced (quicknode-sdk crate in Rust, @quicknode/sdk in Node, quicknode_sdk in Ruby). Python was the odd one out.

Files changed

• pyproject.toml, crates/python/pyproject.toml — maturin module-name
• python/sdk/ → python/quicknode_sdk/ (directory rename via git mv)
• __init__.py, __init__.pyi, init_manual_override.pyi — internal from sdk._core → from quicknode_sdk._core
• All five python/examples/*.py scripts
• python/README.md (6 import examples + error-class import line)
• Root README.md project-structure tree
• CLAUDE.md build/consistency notes
• Justfile python-build recipe paths
• .gitignore paths

Test plan

• just python-build produces wheel for quicknode_sdk._core
• from quicknode_sdk import QuicknodeSdk, ApiError imports cleanly
• import sdk raises ModuleNotFoundError (old name fully removed)
• All five example scripts parse and import (only fail later on missing QN_API_KEY, as expected)
• cargo check && just lint pass
• Reviewer: run just python-build on a clean tree to confirm the maturin/stub-gen step still produces matching _core/__init__.pyi

Linear: DX-5534