`DiagnosticInformation()` wasn't able to take a `std::exception_ptr` due
to the missing conversion on older boost versions, so now everything uses
the std::exception_ptr instead. There are still a few reasons to use
`boost::exception` in some places, but for exception pointers, the standard
one should be better in most cases and almost never requires to include an
extra header.
Since perfdata is set once when a check result is created and
never changed again, locking this is unnecessary. This avoids
components unnecessarily waiting on each other when processing
perfdata.
This fixes the locking cascade observed sometimes when the perfdata
writer work queue blocks, where it extends to a lock on the entire
check result eventually, affecting even more components.
