Add X25519 generateKey overload to SubtleCrypto

[kairosci]

Summary

This PR adds a specific overload for the X25519 key exchange algorithm to the SubtleCrypto.generateKey() method, following the same pattern as the existing Ed25519 overload.

Changes

Added the following overload to SubtleCrypto interface in both dom.generated.d.ts and webworker.generated.d.ts:

generateKey(algorithm: "X25519" | { name: "X25519" }, extractable: boolean, keyUsages: ReadonlyArray<"deriveBits" | "deriveKey">): Promise<CryptoKeyPair>;

Rationale

X25519 is used for key derivation (ECDH), so it uses deriveBits and deriveKey as valid keyUsages, unlike Ed25519 which uses sign and verify.

This allows TypeScript to correctly infer CryptoKeyPair as the return type when using X25519, eliminating the need for type assertions or instanceof checks:

// Before: keyPair is CryptoKey | CryptoKeyPair, requires type assertion
const keyPair = await crypto.subtle.generateKey({ name: "X25519" }, true, ["deriveKey"]);

// After: keyPair is CryptoKeyPair, publicKey is directly accessible
const keyPair = await crypto.subtle.generateKey({ name: "X25519" }, true, ["deriveKey"]);
const publicKey = keyPair.publicKey; // No error!

[typescript-bot]

It looks like you've sent a pull request to update some generated declaration files related to the DOM. These files aren't meant to be edited by hand, as they are synchronized with files in the TypeScript-DOM-lib-generator repository. You can read more here. For house-keeping purposes, this pull request will be closed.

[typescript-bot]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.