minimize temporary strings for better performance

[qiufengshe]

1. use interpolated strings to reduce temporary strings
2. use ReadOnlySpan.Slice instead String.Substring

[love-linger]

Please make your changes based on develop branch.

[qiufengshe]

ok

[love-linger]

I mean you should rebase your code to develop branch first, then create a new PR.

[qiufengshe]

I resubmitted a PR