fix: correct testnet socket stream url

[zeroaddresss]

Problem

The TESTNET_CONFIG uses an incorrect WebSocket URL for private streams:

• Current: wss://starknet.sepolia.extended.exchange/stream.extended.exchange/v1
• Should be: wss://api.starknet.sepolia.extended.exchange/stream.extended.exchange/v1 (source: Extended API docs)

This causes HTTP 401 Unauthorized errors when connecting to private WebSocket streams (e.g., account updates) on testnet.

Solution

Add the api. prefix to the testnet WebSocket URL to match the Extended API documentation

Testing

Tested on Starknet Sepolia testnet:

Before fix:

stream_client.subscribe_to_account_updates(api_key)
# Result: HTTP 401 Unauthorized

After fix:
stream_client.subscribe_to_account_updates(api_key)
# Result: Connection successful, receiving events

[alexex10]

hey @zeroaddresss , appreciate the fix! 🤦 pls fix the formatting and we are good to merge.

[zeroaddresss]

hey @zeroaddresss , appreciate the fix! 🤦 pls fix the formatting and we are good to merge.

done, it was just the LSP autoformatting on-save.
fixed it now :)