CA1845: Use span-based 'string.Concat'

[himgoyalmicro]

Link to issue description: https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1845

Rule Description:

Calling Substring produces a copy of the extracted substring. By using AsSpan instead of Substring and calling the overload of string.Concat that accepts spans, you can eliminate the unnecessary string allocation.