Convert 4 client methods onto request_endpoint (drop dead params)

[martinkersner]

Closes #116

Summary

Converts 4 client methods off hardcoded self.query("/api/v1/...") calls onto self.request_endpoint(op_id, **wire_params), using snake_case wire params from the codegen'd datamaxi/_endpoints.py registry (the live backend contract). Dead kwargs the backend silently ignores are removed from the Python signatures (pre-1.0 cleanup — passing them now raises TypeError). Over-specified mocked tests updated to the real contract.

Premium was pulled from this PR — the registry is incomplete for premium (missing ~35 filter params, incl. known-working token_include/token_exclude; keeps min_sv but not max_sv), so routing it through request_endpoint would silently drop working filters. Tracked separately in #119 (fix camelCase wire bug + expand registry upstream, then convert).

Per method:

• funding_rate.latest — dropped sort, limit (not in registry). Now request_endpoint("funding_rate_latest", exchange=, symbol=).
• cex_token.updates — dropped sort + its ASC/DESC validation; removed now-unused DESC/ASC import. Now request_endpoint("cex_token_updates", page=, limit=, type=). Kept (response, next_request) tuple.
• cex_symbol.volume — dropped exchange. Signature now volume(base).
• cex_symbol.cautions / delistings — dropped base. Kept exchange.

Note: the registry defines additional filters not yet exposed (cex_symbol delistings market/from_ms/to_ms/include_past/limit/page, cautions market/min_level/active_only/limit/page, cex_symbol_volume market); left out to keep scope to the issue. Can be added later.

Test plan

• Updated mocked tests to real contract: test_token_updates_sends_query_params (removed sort assertion), test_volume_sends_base_param (dropped exchange), test_cautions_returns_dict (base → exchange).
• Removed integration cases for removed kwargs: test_updates_sort_asc/desc, test_latest_with_sort, test_latest_with_limit (would TypeError under -m integration).
• Offline suite green: python -m pytest -m "not integration" → 113 passed, 11 skipped, 116 deselected.
• Integration file collects clean; black + flake8 clean on touched files. grep -rn "/api/v" datamaxi/datamaxi/*.py clean except doc-link comments; no self.query( remains in the 4 methods.