fix: align noise-handler buffer types for TypeScript 5.x compatibility

- Add explicit Buffer type annotations to salt, encKey, decKey variables
- Add Promise<[Buffer, Buffer]> return type to localHKDF function
- Add Buffer type casts for subarray return values
- Remove unnecessary non-null assertion operators (!)

Fixes TS2322 type mismatch errors when building with TypeScript 5.9.3+
and Node.js v24+. No runtime behavior changes.

Based on upstream PR #2284.

src/Utils/noise-handler.ts

@@ -64,9 +64,9 @@ export const makeNoiseHandler = ({
 
 	const data = Buffer.from(NOISE_MODE)
 	let hash = data.byteLength === 32 ? data : sha256(data)
-	let salt = hash
-	let encKey = hash
-	let decKey = hash
+	let salt: Buffer = hash
+	let encKey: Buffer = hash
+	let decKey: Buffer = hash
 	let counter = 0
 	let sentIntro = false
 
@@ -116,23 +116,23 @@ export const makeNoiseHandler = ({
 		return result
 	}
 
-	const localHKDF = async (data: Uint8Array) => {
+	const localHKDF = async (data: Uint8Array): Promise<[Buffer, Buffer]> => {
 		const key = await hkdf(Buffer.from(data), 64, { salt, info: '' })
-		return [key.subarray(0, 32), key.subarray(32)]
+		return [key.subarray(0, 32) as Buffer, key.subarray(32) as Buffer]
 	}
 
 	const mixIntoKey = async (data: Uint8Array) => {
 		const [write, read] = await localHKDF(data)
-		salt = write!
-		encKey = read!
-		decKey = read!
+		salt = write
+		encKey = read
+		decKey = read
 		counter = 0
 	}
 
 	const finishInit = async () => {
 		isWaitingForTransport = true
 		const [write, read] = await localHKDF(new Uint8Array(0))
-		transport = new TransportState(write!, read!)
+		transport = new TransportState(write, read)
 		isWaitingForTransport = false
 
 		logger.trace('Noise handler transitioned to Transport state')