Replace the old encode base64 and decode base64 with new-base64 commands (#14018)

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# Description
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Maybe we can deprecate `encode new-base64` and `decode new-base64`
first, to make the code clean and simple I'd rather remove the old
`encode base64` and `decode base64` and replace them with the `*
new-base64` commands.

Related PR: https://github.com/nushell/nushell/pull/13428

# User-Facing Changes
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helps us keep track of breaking changes. -->

- `encode new-base64` --> `encode base64`
- `decode new-base64` --> `decode base64`

# Tests + Formatting
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It's a breaking change

crates/nu-command/tests/commands/base/base64.rs

@@ -2,18 +2,18 @@ use nu_test_support::nu;
 
 #[test]
 fn canonical() {
-    super::test_canonical("new-base64");
-    super::test_canonical("new-base64 --url");
-    super::test_canonical("new-base64 --nopad");
-    super::test_canonical("new-base64 --url --nopad");
+    super::test_canonical("base64");
+    super::test_canonical("base64 --url");
+    super::test_canonical("base64 --nopad");
+    super::test_canonical("base64 --url --nopad");
 }
 
 #[test]
 fn const_() {
-    super::test_const("new-base64");
-    super::test_const("new-base64 --url");
-    super::test_const("new-base64 --nopad");
-    super::test_const("new-base64 --url --nopad");
+    super::test_const("base64");
+    super::test_const("base64 --url");
+    super::test_const("base64 --nopad");
+    super::test_const("base64 --url --nopad");
 }
 
 #[test]
@@ -21,7 +21,7 @@ fn encode() {
     let text = "Ș̗͙̂̏o̲̲̗͗̌͊m̝̊̓́͂ë̡̦̞̤́̌̈́̀ ̥̝̪̎̿ͅf̧̪̻͉͗̈́̍̆u̮̝͌̈́ͅn̹̞̈́̊k̮͇̟͎̂͘y̧̲̠̾̆̕ͅ ̙͖̭͔̂̐t̞́́͘e̢̨͕̽x̥͋t͍̑̔͝";
     let encoded = "U8yCzI/MpsyXzZlvzZfMjM2KzLLMssyXbcyKzJPMgc2CzJ1lzYTMjM2EzIDMpsyhzJ7MpCDMjsy/zYXMpcydzKpmzZfNhMyNzIbMqsy7zKfNiXXNjM2EzK7Mnc2Fbs2EzIrMucyea82YzILMrs2HzJ/NjnnMvsyVzIbNhcyyzKfMoCDMgsyQzJnNlsytzZR0zIHNmMyBzJ5lzL3Mos2VzKh4zYvMpXTMkcyUzZ3NjQ==";
 
-    let outcome = nu!("'{}' | encode new-base64", text);
+    let outcome = nu!("'{}' | encode base64", text);
     assert_eq!(outcome.out, encoded);
 }
 
@@ -30,7 +30,7 @@ fn decode_string() {
     let text = "Very important data";
     let encoded = "VmVyeSBpbXBvcnRhbnQgZGF0YQ==";
 
-    let outcome = nu!("'{}' | decode new-base64 | decode", encoded);
+    let outcome = nu!("'{}' | decode base64 | decode", encoded);
     assert_eq!(outcome.out, text);
 }
 
@@ -40,10 +40,10 @@ fn decode_pad_nopad() {
     let encoded_pad = "4oCdwqUuw6RAwrBiWsO2wqI=";
     let encoded_nopad = "4oCdwqUuw6RAwrBiWsO2wqI";
 
-    let outcome = nu!("'{}' | decode new-base64 | decode", encoded_pad);
+    let outcome = nu!("'{}' | decode base64 | decode", encoded_pad);
     assert_eq!(outcome.out, text);
 
-    let outcome = nu!("'{}' | decode new-base64 --nopad | decode", encoded_nopad);
+    let outcome = nu!("'{}' | decode base64 --nopad | decode", encoded_nopad);
     assert_eq!(outcome.out, text);
 }
 
@@ -53,10 +53,10 @@ fn decode_url() {
     let encoded = "cDpn15jdvt+rdCs/";
     let encoded_url = "cDpn15jdvt-rdCs_";
 
-    let outcome = nu!("'{}' | decode new-base64 | decode", encoded);
+    let outcome = nu!("'{}' | decode base64 | decode", encoded);
     assert_eq!(outcome.out, text);
 
-    let outcome = nu!("'{}' | decode new-base64 --url | decode", encoded_url);
+    let outcome = nu!("'{}' | decode base64 --url | decode", encoded_url);
     assert_eq!(outcome.out, text);
 }
 
@@ -65,9 +65,9 @@ fn reject_pad_nopad() {
     let encoded_nopad = "YQ";
     let encoded_pad = "YQ==";
 
-    let outcome = nu!("'{}' | decode new-base64", encoded_nopad);
+    let outcome = nu!("'{}' | decode base64", encoded_nopad);
     assert!(!outcome.err.is_empty());
 
-    let outcome = nu!("'{}' | decode new-base64 --nopad", encoded_pad);
+    let outcome = nu!("'{}' | decode base64 --nopad", encoded_pad);
     assert!(!outcome.err.is_empty())
 }