feat(examples): add Python payment demo with web3.py

[Wanbogang]

This PR adds a complete Tempo payment demo using web3.py.

Included in this example:

• faucet.py: faucet wrapper helper
• payment.py: payment helper module
• send_tx.py: script for sending a sample transaction
• config.py: configuration loader
• client.py: simple Web3 client wrapper
• __init__.py: package init
• main.py: runnable demo entrypoint
• Smoke test used during development

All files are located under:

examples/tempo-payment-demo/

A sample development transaction hash used during testing:
b98e0912a387612e53d8f4e421b4f201f2019eec9c9ee549168ae4bdd73347d

The goal of this PR is to provide a minimal and clear Python example for developers integrating Tempo payments.

✅ Checklist

• Code follows project style guidelines
• Documentation is complete and accurate
• All files are properly formatted
• No sensitive data (keys, secrets) committed
• Example has been tested on Tempo testnet
• Transaction verified on explorer
• README is comprehensive with examples and troubleshooting
• Ready for maintainer review

🔄 Breaking Changes

None - This is a new example addition.

🔗 Related Issues

N/A - This is a documentation/example contribution to help Python developers integrate with Tempo.

📊 Testing Evidence

Successfully tested on Tempo Testnet:

• ✅ Faucet funding works
• ✅ TIP-20 transfer executes correctly
• ✅ Transaction confirmed and visible on explorer
• ✅ Balance updates properly

Test transaction: https://explore.tempo.xyz/tx/b98e091a23a761e25d8ff4e421ab4f201f2019ecd6c9ee549168ee4bdd73347d