nimiq-keys: Denial of service in Ed25519 multisig delinearization via invalid curve points

### Impact A denial-of-service vulnerability exists in the Ed25519 multisig delinearization code path. `Ed25519PublicKey::delinearize()` in `keys/src/multisig/mod.rs` called `.unwrap()` on curve point decompression, which panics when a public key is constructed from 32 bytes that do not represent a valid point on the Ed25519 curve. `Ed25519PublicKey` construction only validates byte length, not curve membership, so invalid keys can reach the delinearization path and crash the hosting process. A secondary panic existed in `Commitment::From<[u8; 32]>`, which similarly called `.unwrap()` on a failing curve point decompression. **Who is affected:** Browser and desktop wallet users of the web-client WASM library and the `nimiq-wallet` crate, when initiating a multisig operation with an attacker-supplied public key. An attacker must convince the user to include a crafted public key in a multisig setup — this is not a remotely triggerable node/validator crash. **Who is NOT affected:** Validator nodes, consensus, blockchain, mempool, and networking code. There is no on-chain multisig account type; multisig is a purely client-side construct, and no validator/consensus code calls the multisig delinearization path. ### Patches See [PR](https://github.com/nimiq/core-rs-albatross/pull/3713). ### Workarounds No code-level workaround exists short of the patch. Users of wallet applications can mitigate exposure by only performing multisig operations with public keys received from trusted sources. ### Resources - Affected code: `keys/src/multisig/mod.rs`, `keys/src/multisig/commitment.rs`