fix(lint): trailing-label CFG guard and the goroutine alias

Assisted-by: GLM 5.3

lint/lint.go

@@ -12,6 +12,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
 	"sourcedock.dev/petrbalvin/gasm-devkit/asm"
@@ -366,8 +367,9 @@ func lintText(t *ast.Text, tab *arch.Table, archKnown bool, cfg Config, macros m
 		for name, pos := range defined {
 			if _, ok := referenced[name]; !ok {
 				out = append(out, Diagnostic{
-					Pos:      pos,
-					End:      token.Position{Line: pos.Line, Column: pos.Column + len(name)},
+					Pos: pos,
+					// Columns are rune-based, so the end offset is too.
+					End:      token.Position{Line: pos.Line, Column: pos.Column + utf8.RuneCountInString(name)},
 					Severity: Hint,
 					Code:     CodeUnusedLabel,
 					Message:  fmt.Sprintf("label %q is defined but never referenced", name),