Refactor text utilities and expand their usage

This commit refactors existing text utility functions into the
application layer for broad reuse and integrates them across
the codebase. Initially, these utilities were confined to test
code, which limited their application.

Changes:

- Move text utilities to the application layer.
- Centralize text utilities into dedicated files for better
  maintainability.
- Improve robustness of utility functions with added type checks.
- Replace duplicated logic with centralized utility functions
  throughout the codebase.
- Expand unit tests to cover refactored code parts.

tests/unit/application/Context/State/Code/Generation/CodeBuilder.spec.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect } from 'vitest';
 import { CodeBuilder } from '@/application/Context/State/Code/Generation/CodeBuilder';
+import { splitTextIntoLines } from '@/application/Common/Text/SplitTextIntoLines';
 
 describe('CodeBuilder', () => {
   class CodeBuilderConcrete extends CodeBuilder {
@@ -47,10 +48,24 @@ describe('CodeBuilder', () => {
         .appendLine(expected);
       // assert
       const result = sut.toString();
-      const lines = getLines(result);
+      const lines = splitTextIntoLines(result);
       expect(lines[1]).to.equal('str');
     });
-    describe('append multi-line string as multiple lines', () => {
+    describe('append multi-line string correctly', () => {
+      it('appends multi-line string with empty lines preserved', () => {
+        // arrange
+        const sut = new CodeBuilderConcrete();
+        const expectedLines: string[] = ['', 'line1', '', 'line2', '', '', 'line3', '', ''];
+        const multilineInput = expectedLines.join('\n');
+
+        // act
+        sut.appendLine(multilineInput);
+        const actual = sut.toString();
+
+        // assert
+        const actualLines = splitTextIntoLines(actual);
+        expect(actualLines).to.deep.equal(expectedLines);
+      });
       describe('recognizes different line terminators', () => {
         const delimiters = ['\n', '\r\n', '\r'];
         for (const delimiter of delimiters) {
@@ -64,7 +79,7 @@ describe('CodeBuilder', () => {
             sut.appendLine(code);
             // assert
             const result = sut.toString();
-            const lines = getLines(result);
+            const lines = splitTextIntoLines(result);
             expect(lines).to.have.lengthOf(2);
             expect(lines[0]).to.equal(line1);
             expect(lines[1]).to.equal(line2);
@@ -111,7 +126,7 @@ describe('CodeBuilder', () => {
     sut.appendTrailingHyphensCommentLine(totalHyphens);
     // assert
     const result = sut.toString();
-    const lines = getLines(result);
+    const lines = splitTextIntoLines(result);
     expect(lines[0]).to.equal(expected);
   });
   it('appendCommentLine', () => {
@@ -126,7 +141,7 @@ describe('CodeBuilder', () => {
       .appendCommentLine(comment)
       .toString();
     // assert
-    const lines = getLines(result);
+    const lines = splitTextIntoLines(result);
     expect(lines[0]).to.equal(expected);
   });
   it('appendCommentLineWithHyphensAround', () => {
@@ -142,7 +157,7 @@ describe('CodeBuilder', () => {
       .appendCommentLineWithHyphensAround(sectionName, totalHyphens)
       .toString();
     // assert
-    const lines = getLines(result);
+    const lines = splitTextIntoLines(result);
     expect(lines[1]).to.equal(expected);
   });
   describe('currentLine', () => {
@@ -180,7 +195,3 @@ describe('CodeBuilder', () => {
     });
   });
 });
-
-function getLines(text: string): string[] {
-  return text.split(/\r\n|\r|\n/);
-}