This also seems to squash a stubborn space leak we see with
subscriptions (linking to canonical #3388 for reference).
This may also fix some of the "Unexpected exception" websockets
exceptions we are now surfacing (see e.g. #4344)
Also: dev.sh: fix hpc reporting
Initial work on this done by Vamshi.
There are two implementations of a Cache, namely a bounded and an
unbounded variant. This can be elegantly captured in a type class.
In addition to reducing the amount of error-prone code in the
definition of the cache, this version reduces the amount of
error-prone code in usage sites of the cache, as it makes the cache
into an abstract object, so that a calling site cannot distinguish
between cache types. Any decision about what should be cached should
be made through the interface of a cache, rather than at the callsite,
and this is captured by this variant.
These aren't suitable e.g. for running in CI since some take far too
long (and an impossibly long-time when running under criterion's normal
bootstrapping sampling regime.
We might try to improve this ourselves:
https://github.com/bos/criterion/issues/218
An initial summary analysis will be in #3530.
