Deduplicate httpx Timeout construction with match helper in transports

[adamtheturtle]

Summary

Deduplicate httpx timeout construction in vws/transports.py where HTTPXTransport.__call__ and AsyncHTTPXTransport.__call__ each use the same isinstance(request_timeout, tuple) branch.

Precise locations

• File: src/vws/transports.py
• HTTPXTransport.__call__: lines 152–166 (approx.)
• AsyncHTTPXTransport.__call__: lines 275–289 (approx.)

Suggested approach

1. Add a private helper, e.g. _httpx_timeout(request_timeout: float | tuple[float, float]) -> httpx.Timeout, implemented with match request_timeout::
   • case (connect, read): → per-field timeouts
   • case float() | int() as t: → symmetric connect/read (today only float in the annotation, but runtime may pass int from callers — preserve current coercion behavior)
2. Call the helper from both transport classes.

[adamtheturtle]

• Advanced pattern matching support astral-sh/ty#887
• Sequence pattern in match/case does not narrow tuple out of a union facebook/pyrefly#3147

These caused issues when trying to do this