feat: expand async client to the full resource tree (#142)

[martinkersner]

Follow-up to the async pilot (#149) — mirrors the entire sync surface in async, as requested.

Restructure + coverage

datamaxi/aio is now a package:

• _core.py — AsyncAPI, AsyncResource
• cex.py — candle, ticker, fee, wallet_status, announcement, token, symbol
• funding_rate.py, forex.py, premium.py, liquidation.py, open_interest.py, margin_borrow.py, index_price.py
• telegram.py (AsyncTelegram), naver.py (AsyncNaver) — standalone top-level clients
• __init__.py — AsyncDatamaxi full tree + re-exports + __all__

Every sync public method is mirrored (~50 methods): cex.{candle,ticker,fee,wallet_status,announcement,token,symbol}.*, funding_rate.{history,latest,exchanges,symbols}, forex, premium, liquidation.{__call__,feed,heatmap,map,stats,symbol_history}, open_interest.{__call__,list,overview,summary,history_aggregated}, margin_borrow, index_price, AsyncTelegram.{channels,messages}, AsyncNaver.{symbols,trend}.

How it stays faithful

• Each method is async def + await self.request_endpoint(...) with the same op_ids, params (incl. **{"from":...,"to":...}), validation, and return shaping as sync.
• Pagination next_request closures are async (async def ... return await self.<method>(...)).
• pandas / convert_data_to_data_frame imports stay lazy; typed response models reused for return hints.
• The whole tree shares one AsyncAPI/httpx client (verified). AsyncTelegram/AsyncNaver build their own, matching sync.
• No sync code changed. httpx is still the optional [async] extra; import datamaxi doesn't load it.

Judgment calls (from the port)

• AsyncTelegram/AsyncNaver subclass AsyncResource but override __init__ to build their own transport + add context-manager/__repr__ — cleanest way to be standalone yet reuse request_endpoint/last_response.
• Sync's cosmetic __module__/__qualname__ reassignments (a few resources set them in __init__) weren't replicated — the async resources have no __init__; behavior is unaffected.

Tests

• New tests/test_async_resources.py (10) via one path-routing httpx.MockTransport: a representative method per resource (raw / pandas=False returns) + the async pagination closures (announcement, telegram, funding history) are awaitable.
• Combined with the pilot's test_async.py, every async resource is exercised.
• pytest -m "not integration": 172 passed, 11 skipped.
• black + flake8 clean; sync import datamaxi still doesn't load httpx.

Known failures

None.