global: Fix or suppress most lints/warnings

Signed-off-by: Samuel Holland <samuel@sholland.org>

app/src/main/java/com/wireguard/crypto/KeyEncoding.java

@@ -6,12 +6,17 @@ package com.wireguard.crypto;
  * This is a specialized constant-time base64 implementation that resists side-channel attacks.
  */
 
-public class KeyEncoding {
+@SuppressWarnings("MagicNumber")
+public final class KeyEncoding {
     public static final int KEY_LENGTH = 32;
     public static final int KEY_LENGTH_BASE64 = 44;
     private static final String KEY_LENGTH_BASE64_EXCEPTION_MESSAGE =
             "WireGuard base64 keys must be 44 characters encoding 32 bytes";
 
+    private KeyEncoding() {
+        // Prevent instantiation.
+    }
+
     private static int decodeBase64(final char[] src, final int src_offset) {
         int val = 0;
         for (int i = 0; i < 4; ++i) {

app/src/main/java/com/wireguard/crypto/Keypair.java

@@ -6,6 +6,7 @@ import java.security.SecureRandom;
  * Represents a Curve25519 keypair as used by WireGuard.
  */
 
+@SuppressWarnings("MagicNumber")
 public class Keypair {
     private final byte[] privateKey;
     private final byte[] publicKey;