feat: add demo trading support

[carlosmiei]

• Fixes proxy use for websockets
• Adjusts mock tests for demo domain
• Feat: allows running tests in parallel
• Simplifies code by using tox instead of both tox and github action matrix strategy
• Update github action verions

[Copilot]

Pull Request Overview

This PR adds demo trading support to the Binance client library, providing an alternative to the existing testnet functionality. The change introduces a new demo parameter that can be used alongside or instead of the testnet parameter to connect to Binance's demo trading environment.

• Adds demo URL constants for all trading endpoints (spot, futures, coin futures, websockets)
• Introduces demo parameter to client constructors and base client initialization
• Updates URL selection logic to prioritize testnet over demo when both are enabled
• Updates documentation to reflect demo trading support and mark testnet as deprecated

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
binance/base_client.py	Adds demo URL constants and demo parameter support with URL selection logic
binance/client.py	Adds demo parameter to synchronous client constructor
binance/async_client.py	Adds demo parameter to asynchronous client constructor and factory method
binance/ws/streams.py	Implements demo websocket URL selection across all socket manager methods
README.rst	Updates documentation to mention demo trading support and mark testnet as deprecated

Comments suppressed due to low confidence (1)

binance/client.py:8677

• The URL field has been cleared to an empty string, which appears unrelated to the demo trading feature. This change should be reverted or explained in the commit message if intentional.

                "url": "",

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[Copilot]

Pull Request Overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

binance/client.py:8748

• [nitpick] The URL field has been cleared to an empty string. This could cause issues for consumers expecting a valid URL. Consider using a placeholder URL or documenting this as intentional for demo purposes.

                "url": "",

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