Like other backends use the `AsyncClient` for all venue specific
client-sessions but change to allocating them inside `get_client()`
using an `AsyncExitStack` and inserting directly in the
`Client.venue_sesh: dict` table during init.
Supporting impl tweaks:
- remove most of the API client session building logic and instead make
`Client.__init__()` take in a `venue_sessions: dict` (set it to
`.venue_sesh`) and `conf: dict`, instead opting to do the http client
configuration inside `get_client()` since all that code only needs to
be run once.
|_load config inside `get_client()` once.
|_move session token creation into a new util func `init_api_keys()` and
also call it from `get_client()` factory; toss in an ex. toml section
config to the doc string.
- define `_venue_urls: dict[str, str]` (content taken from old static
`.venue_sesh` dict) at module level and feed them as `base_url: str`
inputs to the client create loop.
- adjust all call sigs in httpx-sesh-using methods, namely just
`._api()`.
- do a `.exch_info()` call in `get_client()` to cache the symbology
set.
Unrelated changes for various other outstanding buggers:
- to get futures feeds correctly loading when selected
from search (like 'XMRUSDT.USDTM.PERP'), expect a `MktPair` input to
`Client.bars()` such that the exact venue-key can be looked up (via
a new `.pair2venuekey()` meth) and then passed to `._api()`.
- adjust `.broker.open_trade_dialog()` to failover to paper engine when
there's no `api_key` key set for the `subconf` venue-key.
ab1463d942