feat: Add ed25519 key derivation and signature functions

[FrederikBolding]

Explanation

Add public key derivation and signing utilities for Ed25519.

React Native benchmarks:

Finished ed25519 public key benchmark (cold): WebCrypto = 38 ms JS = 1167 ms

Finished ed25519 signing benchmark using 1000 bytes of data: WebCrypto = 2 ms JS = 102 ms
Finished ed25519 signing benchmark using 5000 bytes of data: WebCrypto = 9 ms JS = 279 ms
Finished ed25519 signing benchmark using 10000 bytes of data: WebCrypto = 2 ms JS = 504 ms

Finished ed25519 verification benchmark using 1000 bytes of data: WebCrypto = 2 ms JS = 89 ms
Finished ed25519 verification benchmark using 5000 bytes of data: WebCrypto = 2 ms JS = 180 ms
Finished ed25519 verification benchmark using 10000 bytes of data: WebCrypto = 1 ms JS = 295 ms

References

https://consensyssoftware.atlassian.net/browse/WPC-1344

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Introduces new signing and verification primitives in a cryptography package; behavior is WebCrypto-backed and test-vector covered, but consumers must handle keys and signatures correctly.

Overview
Adds a new @metamask/cryptography/ed25519 export with getPublicKey, sign, and verify, implemented on crypto.subtle with raw 32-byte keys and 64-byte signatures, PKCS#8 wrapping for private keys, and strict length checks.

Shared buildPKCS8Header / toPKCS8 helpers in utils.ts replace the inline X25519 PKCS8 construction so X25519 and Ed25519 use the same envelope pattern. Changelog and package.json exports document the new subpath; tests cover RFC 8032 vector 3 plus BufferSource variants and invalid key/signature sizes.

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[FrederikBolding]

We could parse jwk.x manually, but it seemed cleaner to let the WebCrypto API deal with it instead. Potentially faster too?

[Mrtenz]

Maybe this?

Suggested change

	export function buildPKCS8Header(
	export function buildPkcs8Header(

[FrederikBolding]

I had it cased like this before but kinda preferred the uppercase option 🤔