basenc: implement --base58 encoding option (#8751)

* basenc: implement --base58 encoding option

Add support for Base58 encoding to basenc as per GNU coreutils 9.8.
Base58 uses the alphabet '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
which excludes visually ambiguous characters (0, O, I, l).

Resolves issue #8744.

* basenc: fix clippy warnings and spelling issues

Fix explicit iteration clippy warnings. Add Base58 alphabet to spell-checker ignore list to resolve cspell errors.

tests/by-util/test_basenc.rs

@@ -185,21 +185,30 @@ fn test_base2lsbf_decode() {
 }
 
 #[test]
-fn test_choose_last_encoding_z85() {
+fn test_z85_decode() {
     new_ucmd!()
-        .args(&[
-            "--base2lsbf",
-            "--base2msbf",
-            "--base16",
-            "--base32hex",
-            "--base64url",
-            "--base32",
-            "--base64",
-            "--z85",
-        ])
-        .pipe_in("Hello, World")
+        .args(&["--z85", "-d"])
+        .pipe_in("nm=QNz.92jz/PV8")
         .succeeds()
-        .stdout_only("nm=QNz.92jz/PV8\n");
+        .stdout_only("Hello, World");
+}
+
+#[test]
+fn test_base58() {
+    new_ucmd!()
+        .arg("--base58")
+        .pipe_in("Hello, World!")
+        .succeeds()
+        .stdout_only("72k1xXWG59fYdzSNoA\n");
+}
+
+#[test]
+fn test_base58_decode() {
+    new_ucmd!()
+        .args(&["--base58", "-d"])
+        .pipe_in("72k1xXWG59fYdzSNoA")
+        .succeeds()
+        .stdout_only("Hello, World!");
 }
 
 #[test]
@@ -238,6 +247,15 @@ fn test_choose_last_encoding_base2lsbf() {
         .stdout_only("00110110110011100100011001100110\n");
 }
 
+#[test]
+fn test_choose_last_encoding_base58() {
+    new_ucmd!()
+        .args(&["--base64", "--base32", "--base16", "--z85", "--base58"])
+        .pipe_in("Hello!")
+        .succeeds()
+        .stdout_only("d3yC1LKr\n");
+}
+
 #[test]
 fn test_base32_decode_repeated() {
     new_ucmd!()