The documentation for that specific module even calls it out as "painfully hard-coded biquad filter code", YMMV.
I'd guess those files aren't what the author actually edits - there are commits that suggest that they are _generated_ from "boilerplate", and even a few files that seem to have failed interpolations ("__MyCompanyName__" in some copyright lines, for instance)
A lot of files also seem to have duplicated code, down to individual comments. For instance, the comment on line 24 reoccurs on line 344 of this effect: