Added files to allow this proof to be ran on the external CI

[JoaoDiogoDuarte]

Hi all, I added two files to allow this proof to be added to the Easycrypt external CI.

As this repository will eventually have the ed25519 proof, I added both the tests.config and easycrypt.project to the proof/crypto_scalarmult/curve25519/ folder.

The external CI would effectively run in the working directory proof/crypto_scalarmult/curve25519/:

easycrypt runtest tests.config curve25519 

To avoid multiple tests.config files when we have the ed25519 proof, I could move said file to the proof/ directory so that the external CI would run easycrypt runtest ../../tests.config curve25519.

In my Easycrypt fork, I added the following to the external.json file and made a PR EasyCrypt/easycrypt#642:

 { "name"       : "curve25519"
  , "repository" : "https://github.com/formosa-crypto/formosa-25519"
  , "branch"     : "main"
  , "subdir"     : "proof/crypto_scalarmult/curve25519"
  , "config"     : "tests.config"
  , "scenario"   : "curve25519"
  , "options"    : ""
  }

Please provide feedback and if everything looks good, I can go ahead and make

[tfaoliveira-sb]

It looks good. @strub ?

I recently updated the image running the CI such that it is able to run runtest.

And I pushed into this branch an update to the Makefile and workflow with a corresponding rule/job.

If everything is fine on the EasyCrypt side I can do the switch in the workflow.

Note: we are using 2024.01; migrating to 2024.09, figuring out provers versions, and Jasmin 2024.7.01 can be done in separate PR. I didn't found the flag -jobs in 2024.01 for runtest. This can be delayed as well.