fix(client): extend session-key relayer timeout

[kartojal]

Extends the relayer read timeout to five minutes for sync and async session-key authorization and revocation submissions. Transaction and registry polling timeouts remain unchanged.

Tests: uv run pytest tests/unit/test_session_key_authorization.py

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Note

Low Risk
Scoped timeout override for session-key relayer POSTs only; no auth or signing logic changes.

Overview
Session-key authorize and revoke submissions can block on the relayer while it validates, simulates, persists, and broadcasts, so the default 10s HTTP read timeout was too short.

This PR passes a dedicated httpx.Timeout (300s read) into post_json for both async and sync _post_session_key_operation helpers. Connect, write, and pool limits stay modest; transaction and registry polling still use existing relayer poll settings.

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