Add live WS test for liquidation/feed (firehose)

[martinkersner]

What

Add a live integration test in tests/test_ws_live.py for the liquidation_feed firehose channel (/liquidation/feed, ws.liquidation_feed.stream()).

Why

liquidation_feed is the only SDK-exposed WS channel with no live-lane coverage after #181/PR #182 (which added ticker spot/futures, premium, forex, funding_rate, open_interest, plus the pre-existing liquidation/announcement quiet-window tests).

It couldn't get a deterministic data-assertion because the feed is event-driven: a freshly-connected client isn't guaranteed any data within a bounded window (busy in volatile markets, silent in calm ones).

Options

1. Quiet-window-tolerant stopgap now — mirror the existing test_ws_liquidation_subscribe_tolerates_quiet_window pattern: connect + stream(), assert no error; silence within the timeout = PASS; if a message arrives, assert it's a well-formed liquidation dict. Gives connect/auth/firehose-wiring coverage today, zero flake risk.
2. Hard data-assertion once backend replays on connect — blocked on Bisonai/datamaxi-backend#7990 (feed replays last N liquidations on connect). Once that lands, a fresh connection deterministically yields data and this can become a real data-assert like ticker/premium.

Recommend doing (1) now and upgrading to (2) after #7990.

Done when

tests/test_ws_live.py has a test exercising ws.liquidation_feed.stream() under the integration marker (needs DATAMAXI_API_KEY), deselected from the keyless lane. Quiet window = PASS until backend#7990 enables a deterministic data assertion.

Refs

• Add live WS test asserting real data on a high-traffic channel #181 / PR test(ws): live ticker data assertion on high-traffic channel (Closes #181) #182 (WS live-test coverage)
• Bisonai/datamaxi-backend#7990 (replay last N on connect — unblocks the hard assertion)

[martinkersner]

Closed by PR #202 (merged as 4415921), which also closes #201.

This issue asked for live-lane coverage of ws.liquidation_feed.stream() — option (1) a quiet-window-tolerant stopgap now, upgrading to (2) a hard data-assert once Bisonai/datamaxi-backend#7990 landed.

#7990 shipped and is deployed, so #202 delivers option (2) directly and skips the stopgap: test_ws_liquidation_feed_replays_on_connect in tests/test_ws_live.py asserts a well-formed payload plus snap: true replay frames, with a quiet window as a FAIL. Verified against production — 9/9 live WS tests pass.

The 'Done when' of this issue is satisfied.