We're copying `std::string` objects that know their length. There's no
reason to force a call to `strlen`.

Avoid copying the vector of symbols where possible. When no filter
string is applied we no longer copy the entire vector symbols by having
the symbols used for display be indirected via a pointer. It points
either to the unfiltered symbols or the filtered symbols.

Some unncessary copies have been removed by using `std::move` where
appropriate.

Filtering has been updated to avoid `std::vector::reserve` /
`std::vector::shrink_to_fit` in favor of letting the filtered vector
control its own growth and reuse its buffer. This avoids allocating a
~100MB buffer every time we update the filter only to later reallocate
and move the contents into a smaller buffer. Instead the buffer grows
via `std::vector`'s usual growth algorithm and it is preserved across
filter calls to avoid unnecessarily reallocating it, and only shrink the
buffer if it has shrunk significantly vs previous iterations.