* implement correct Etag and If-None-Match handling, responding with
304 Not Modified if they match
* introduce SessionState and State string type aliases to ensure we are
using the correct fields for those, respectively
* extract the SessionState from the JMAP response bodies in the
groupware framework instead of having to do that in every single
groupware API
* use uint instead of int in some places to clarify that the values are
>= 0
* trace-log how long a Session was held in cache before being evicted
* add Trace-Id header handling: add to response when specified in
request, and implement a custom request logger to include it as a
field
* implement a more compact trace-logging of all the methods and URIs
that are served, to put them into a single log entry instead of
creating one log entry for every URI
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