docs(evm): fix broken viem import, migrate Hardhat guide to v3, add Python quickstart

[alexander-sei]

What & why

Several EVM docs shipped code that fails when run verbatim. These fixes were verified against the live Sei RPC and a fresh hardhat@3.7.0 project.

Fixes

• Broken viem chain import (16 files). import { sei } from '@sei-js/precompiles/viem' doesn't resolve — the published @sei-js/precompiles has no /viem subpath and no sei export, so every viem snippet throws on import. Switched to viem's built-in import { sei } from 'viem/chains' and tightened the viem-quickstart install to npm install viem.
• Unrunnable read snippets. The viem/ethers "first milestone" used an invalid '0xYourAddress' placeholder that throws; replaced with a real example address.
• Hardhat guide migrated to Hardhat 3. The guide shipped a Hardhat 2 config that fails to compile under the Hardhat 3 it tells you to install. Now uses plugins: [hardhatToolboxMochaEthers], type: 'http' networks, configVariable + keystore for secrets, and network.getOrCreate() in tests and scripts.
• UUPS upgrades, plugin-free. @openzeppelin/hardhat-upgrades is Hardhat 2-only, so the upgradeable flow now deploys an ERC1967 proxy directly and upgrades via UUPS upgradeToAndCall. Also dropped __UUPSUpgradeable_init(), which was removed in OpenZeppelin v5 and no longer compiles.
• networks.mdx now links plain-text RPC endpoints (/learn/dev-chains, /learn/rpc-providers) alongside the interactive widget.
• New Python (web3.py) quickstart page wired into the nav; removed the duplicated inline Python sections from the viem/ethers quickstarts.
• npx tsx run instructions added to the TypeScript quickstarts.

Verification

• viem / ethers / web3.py read snippets run against live mainnet (chain ID 1329).
• Hardhat 3 guide verified on hardhat@3.7.0: compile, test, ERC20 Ignition deploy, ERC721 script run, and the full UUPS deploy → upgradeToAndCall → V2 cycle.

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[cursor]

PR Summary

Low Risk
Documentation-only changes with no runtime or on-chain behavior; residual risk is outdated snippets elsewhere (e.g. deploy-verify still shows Hardhat 2-style config) confusing readers.

Overview
This PR fixes copy-pasteable Sei EVM docs: broken viem chain imports, a Hardhat guide that didn’t match Hardhat 3, and clearer onboarding for Python and network RPCs.

viem / wagmi examples (many files) now use import { sei } from 'viem/chains' instead of @sei-js/precompiles/viem, and the viem quickstart install is npm install viem only. “First milestone” read snippets use a valid example address instead of 0xYourAddress. viem/ethers quickstarts add npx tsx run instructions and drop duplicated inline Python in favor of the new page.

Hardhat (evm-hardhat.mdx) is rewritten for Hardhat 3: npx hardhat --init, ESM, plugins: [hardhatToolboxMochaEthers], HTTP networks with configVariable('SEI_PRIVATE_KEY') + keystore (replacing .env/dotenv), and scripts/tests via network.getOrCreate(). UUPS no longer depends on @openzeppelin/hardhat-upgrades; it documents manual ERC1967 deploy and upgradeToAndCall, and removes __UUPSUpgradeable_init for OpenZeppelin v5.

New evm/python-quickstart.mdx (web3.py read/send/contract) is added to Smart Contracts nav in docs.json. networks.mdx links plain-text RPC docs alongside the widget.

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