Wrap requests.post() in create_session() for browser_use, browserbase,
and firecrawl providers with requests.RequestException handling.
Connection timeouts and DNS resolution failures now surface as clean
RuntimeError messages instead of raw requests exception tracebacks.
Browser Use managed-gateway mode preserves raw exception propagation
so the existing idempotency-key retry semantics keep working.
Closes#2746
Co-authored-by: teknium1 <127238744+teknium1@users.noreply.github.com>
13c72fb486