Performance issue when extracting large expression with vecs

[saulshanabrook]

There is currently a performance issue when extracting a large expression with vecs in it.

This PR (#492) adds an example of such a file to the test suite.

I was able to profile the file with samply and can share the performance results:

samply record ./target/profiling/egglog --dont-print-messages tests/eqsat-basic.egg 

Around 20% of the time is spent in TermDag::to_string. We should add a way to disable printing extracting values to strings, because when using with the Python bindings, this work is thrown away.

The remaining 80% is spent in Extract::find_best with about a third inside of that spent in VecSort::extract_expr, ptr::drop_in_place<GenericExpr>, and TermDag::expr_to_term.

[saulshanabrook]

Wow, when I disable printing messages in #492 and use the rewrite of extraction in #495, the time for this benchmark goes down to 400ms!

$ time env RUST_LOG=error ./target/release/egglog --dont-print-messages tests/extract-vec-bench-no-messages.egg 

________________________________________________________
Executed in  391.50 millis    fish           external
   usr time   41.04 millis  189.00 micros   40.85 millis
   sys time    4.21 millis  711.00 micros    3.50 mills