To fit with the rest of the new requirements added in `.data.validate`
this adds `FeedInit` init including `MktPair` and `Asset` loading for
all spot currencies provided by `kucoin`.
Deatz:
- add a `Currency` struct and accompanying `Client.get_currencies()` for
storing all asset infos.
- implement `.get_mkt_info()` which loads all necessary accounting and
mkt meta-data structs including adding `.price/size_tick` fields to
the `KucoinMktPair`.
- on client boot, async spawn requests to cache both symbols and currencies.
- pass `subscribe()` as the `fixture` arg to `open_autorecon_ws()`
instead of opening it manually.
Other:
- tweak `Client._request` to not expect the prefixed `'/'` for the
`endpoint: str`.
- change the `api_v` arg to just be `api: str`.
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