(ngx-features-viewer) Test performance

[damiclem]

It is suspected that the features viewer lags in some occasions, namely:

1. When multiple nested sub-traces are defined
2. When some traces are empty, which might lead to errors
3. When big sequences are used as input, this might lead to an exploding number of calculations (especially with respect to the number of letters to be shown/hidden).

Test performance using Lighthouse 🚨 to have a quick overview.