fix: normalize NamedGroup string for X25519 and X448 to IANA names

[UnaPibaGeek]

Summary

This PR updates the string representation of CurveID 29 and 30 in tls/tls_names.go

• ecdh_x25519 → x25519
• ecdh_x448 → x448

Technical details

CurveID values represent TLS NamedGroup identifiers. According to the IANA TLS NamedGroup registry and RFC 8446, the canonical names for groups 29 and 30 are:

• 29 → x25519
• 30 → x448

The previous labels (ecdh_x25519 and ecdh_x448) were legacy/temporary naming conventions.

This mismatch causes downstream schema validation failures in tools (zgrab2) that validate server_hello.key_share.name against the standard NamedGroup enum.

This seems to be the cause of the test integration failure in this zgrab2 PR: zmap/zgrab2#672, where the error is: zschema.keys.DataValidationException: name: the value ecdh_x25519 is not a valid enum option. This PR is an attempt to fix that error.

[UnaPibaGeek]

cc @dadrian maybe with this minor fix... this time it works out crossing fingers.