feat: Enhance Nostr chat encryption with key validation and logging

- Implement validation for private and public keys before encryption, ensuring they are present and in the correct hex format.
- Add detailed console logging for key lengths and encryption success, improving debugging and transparency in the message encryption process.
- Refactor the encryption call to use validated keys, enhancing security and reliability.

src/lib/utils/crypto.ts

@@ -6,16 +6,26 @@
  * Convert hex string to Uint8Array
  */
 export function hexToBytes(hex: string): Uint8Array {
+  if (typeof hex !== 'string') {
+    throw new TypeError('hexToBytes: expected string, got ' + typeof hex)
+  }
+  
   if (hex.length % 2 !== 0) {
-    throw new Error('Hex string must have even length')
+    throw new Error('hexToBytes: received invalid unpadded hex')
   }
   
-  const bytes = hex.match(/.{2}/g)?.map(byte => parseInt(byte, 16))
-  if (!bytes) {
-    throw new Error('Invalid hex string')
+  const array = new Uint8Array(hex.length / 2)
+  for (let i = 0; i < array.length; i++) {
+    const j = i * 2
+    const hexByte = hex.slice(j, j + 2)
+    const byte = Number.parseInt(hexByte, 16)
+    if (Number.isNaN(byte) || byte < 0) {
+      throw new Error('Invalid byte sequence')
+    }
+    array[i] = byte
   }
   
-  return new Uint8Array(bytes)
+  return array
 }
 
 /**