replace ecdsa with cryptography

[dotlambda]

ecdsa is vulnerable to CVE-2024-23342 and shouldn't be used anyway:

I don't want people to use this library in production environments...

It's a teaching tool, it's a testing tool, it's absolutely not an production grade implementation.
I maintain it to have support for ECDH and ECDSA in tlsfuzzer, which I need to be first and foremost portable. Security does not even enter a picture for that tool.

If you need enterprise grade implementation you should use pyca/cryptography.

• CVE-2024-23342 Timing Attack tlsfuzzer/python-ecdsa#330