Add exchange name translation in `.ib.venues.has_holiday()` to handle
non-standard exchange codes when looking up holiday gaps..
Deats,
- add an ad-hoc lookup dict to remap an IB `Contract.primaryExchange` val
which doesn't exist in the `exchange_calendars`'s alias set.
- use `.get()` with fallback to map `exch` to new `std_exch` and pass
that to `xcals.get_calendar()`.
- add the case i just caught, `'ARCA'` -> `'ARCX'` to the table when i loaded
the `gld.arca.ib` market..
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code