nix: complete jwt loadtests

Completes the jwt loadtests, now we have non-cached, cached + worst case
for the cache.

- jwt-hs (edited): now has the cache disabled
- jwt-hs-cache: cache enabled for jwt-hs
- jwt-hs-cache-worst: worst case of the jwt-hs cache
- jwt-rsa (edited): now has the cache disabled
- jwt-rsa-cache: cache enabled for jwt-rsa
- jwt-rsa-cache-worst: worst case of the jwt-rsa cache

Also deletes `nix/tools/generate_targets_rsa.py` and uses a single
python script.

Should prove what's mentioned on
https://github.com/PostgREST/postgrest/pull/4084#issuecomment-2998170423

.github/workflows/test.yaml

@@ -113,7 +113,7 @@ jobs:
   loadtest:
     strategy:
       matrix:
-        kind: ['mixed', 'jwt-hs', 'jwt-rsa']
+        kind: ['mixed', 'jwt-hs', 'jwt-hs-cache', 'jwt-hs-cache-worst', 'jwt-rsa', 'jwt-rsa-cache', 'jwt-rsa-cache-worst']
     name: Loadtest
     runs-on: ubuntu-24.04
     steps: