refactor: renaming Ed25519 to Edwards25519

[SimonRastikian]

Follow up to #2396.

Partly Closes #2322 namely the section related to renaming Ed25519 into the real curve name Curve25519.

[claude]

PR title type suggestion: This PR renames a curve variant across the codebase without changing functionality, which is a refactoring task. The title should include a conventional commit type prefix.

Suggested title: refactor: rename Ed25519 to Curve25519

[claude]

Code Review: refactor: renaming ed25519 to Curve25519

Straightforward rename of the internal Curve::Ed25519 variant to Curve::Curve25519 across the codebase. The change is mechanical and consistent.

Compatibility Analysis

• Borsh (on-chain state): Safe. Borsh uses variant indices, not names. The variant remains at position 1.
• JSON deserialization: Safe. #[serde(alias = "Ed25519")] preserves backward compatibility for callers passing "Ed25519" to vote_add_domains.
• JSON serialization: The internal Curve enum will now serialize as "Curve25519" instead of "Ed25519". This does NOT affect external consumers because the public API view functions go through the DTO mapping (Curve::Curve25519 => SignatureScheme::Ed25519 at crates/contract/src/dto_mapping.rs:518).
• Node code: The Curve enum is only used in-memory for match arms/logic within the node — no cross-node serialization of this type.

Minor observation (non-blocking)

The existing test_serialization_format test at crates/contract/src/primitives/domain.rs:409 only tests Curve::Secp256k1. Adding a case for Curve::Curve25519 would document the new serialization output ("Curve25519") and catch any future regressions. This is optional since the DTO layer is the actual external contract.

No critical issues found.

✅ Approved

[netrome]

Sorry I thought I approved this already. Nice stuff!

[netrome]

Please rebase/merge latest main and I'll re-approve

The base branch was changed.

[barakeinav1]

is this an external interface change?
what is the impact of it?

[barakeinav1]

same question as above

[barakeinav1]

I see you updated the contract snap, does this mean those changes have a interface breaking change?
and if yes, what is the impact of it?