Task: Add ReadOnlySpan<char> as a char sequence type to the T4 templates

[NightOwl888]

We will need the ReadOnlySpan<char> overloads to optimize utility methods and avoid Substring() calls, which are extremely slow in .NET compared to Java. This requires updating the CodeGenerationSettings.xml file to include them and editing the T4 templates to correctly generate the overloads.

• Methods that contain parameters for startIndex, endIndex, limit, length should omit these parameters and rely on the Slice() method of ReadOnlySpan<char> instead.

It would be best to wait until #40 is done before working on this task.