Fix trade websocket payload types

[koriyoshi2041]

Closes #327.

The live trades websocket payload represents sz as a string and includes tid and a two-user tuple. The official Rust SDK models the same payload as sz: String, tid: u64, and users: (String, String), so this updates the Python Trade TypedDict to match that wire contract.

Validation:

• uvx mypy hyperliquid/utils/types.py
• uvx black --check hyperliquid/utils/types.py
• python -m compileall -q hyperliquid/utils/types.py
• git diff --check