Operation request: Sign/Verify with ECDSA

## Summary
Similar to RSA, support "Sign with ECDSA" and "Verfiy with ECDSA"

### Example Input
the needed key for the operation (sign=>private key | verify => public key) as PEM
the hash operation (SHA256, SHA384, SHA512)

for sign the message is the input
for verify the signature is the input (and the message is provided as option)

### Example Output
for sign: the signature
for verify: the verification result

The issue names no files or tests; start by locating CyberChef's existing RSA signing and verification operations and their tests. Compare their inputs and outputs with the requested PEM keys, SHA-256/SHA-384/SHA-512 choices, message, and signature, then verify that both ECDSA operations produce the specified signature or verification result.

Written by the indexing model from the issue text.