improve the _atomic_ benchmark plots

this MR improves the "atomic" script in benches/README.md to allow filtering species to show in the multibar plot.

in addition to this, the warmup time and the number of samples of Criterion have been increased back to 3sec and 100 respectively.

Note
the benchmarks take 15min on my machine, i.e. by running the following two commands in Nushell

cargo criterion --output-format verbose --message-format json --bench field_operations out> field.ndjson
cargo criterion --output-format verbose --message-format json --bench curve_group_operations out> curve.ndjson

results