There were some imports missing or unused as well as a variety of spots
that had grokability issues due to missing type hints.
Other tweaks as part some more thorough manual testing:
- always raise when not `brokers.toml` section since the API can never
work (no free data without keys).
- inline the `Asset.atype='crypto_currency` field despite it maybe not
being the best value for `OptionPair` instruments..
- tossed in a now-masked pause block for debugging history queries in
`Client.bars()`.
- commented out all the live order ctl (internal) endpoints for now
since they're unused.
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