dont' hardcode curves in the benchmarks

up until now, elliptic curves have been hardcoded in the benchmarks, forcing to run them on all supported curves...

this MR makes it possible to use only a subset of curves.

Note
when running the same commands from !104 (merged), minus the "inbreeding" ones which are not affected by this MR, the time goes from 12min 33sec to 4min 28sec

TODO

• setup
• commit
• recoding
• fec
• linalg
• setup size
• field operations
• group operations

Note
because all the unticked bullet points above are far from critical to the paper and do require to measure all curves, i won't change these for now

examples/benches/README.md

@@ -157,7 +157,7 @@ gplt plot ...[
         ...[100, 1_000, 10_000]
         --shards $k
         --ks $k
-        --curve bls12381
+        --curves bls12381
     ] | from ndnuon | to ndjson out>> recoding.ndjson
 }
 ```
@@ -233,7 +233,7 @@ gplt plot ...[
         -k $k
         -n 1
         --nb-measurements 100
-        --curve bls12381
+        --curves bls12381
     ] | from ndnuon | to ndjson out>> fec.ndjson
 }
 ```