[parsing] Allow digits in mfm fn node function names

Iceshrimp.Parsing/Mfm.fs

@@ -276,7 +276,7 @@ module private MfmParser =
         |>> fun e -> MfmEmojiCodeNode(e) :> MfmNode
 
     let fnNode =
-        skipString "$[" >>. many1Chars asciiLower
+        skipString "$[" >>. many1Chars (asciiLower <|> digit)
         .>>. opt (skipChar '.' >>. sepBy1 fnArg (skipChar ','))
         .>> skipChar ' '
         .>>. many1Till inlineNode (skipChar ']')

Iceshrimp.Tests/Parsing/MfmTests.cs

@@ -349,7 +349,7 @@ public class MfmTests
 	public void TestFn()
 	{
 		const string input =
-			"test $[] $[test] $[test ] $[test test] $[test.a test] $[test.a=b test] $[test.a=b,c=e test] $[test.a,c=e test] $[test.a=b,c test]";
+			"test $[] $[test] $[test ] $[test test] $[test123 test] $[test.a test] $[test.a=b test] $[test.a=b,c=e test] $[test.a,c=e test] $[test.a=b,c test]";
 
 		var some = FSharpOption<IDictionary<string, FSharpOption<string>>>.Some;
 		var none = FSharpOption<IDictionary<string, FSharpOption<string>>>.None;
@@ -363,6 +363,10 @@ public class MfmTests
 			              none,
 			              test),
 			new MfmTextNode(" "),
+			new MfmFnNode("test123",
+			              none,
+			              test),
+			new MfmTextNode(" "),
 			new MfmFnNode("test",
 			              some(new Dictionary<string, FSharpOption<string>>{ {"a", FSharpOption<string>.None} }),
 			              test),