Pull request

Choose Correct

• [x] bug
• [x] feature

Describe the pull request

This PR maybe fixes #418

It adds the namespace and change const to consteexpr in the generated ...._common.hpp file

To Reproduce

See #418

Expected behavior

Screenshots

Desktop (please complete the following information):

• OS:
• eRPC Version:

Steps you didn't forgot to do

• [x] I checked if other PR isn't solving this issue.
• [x] I read Contribution details and did appropriate actions.
• [x] PR code is tested. => But issues with clang and mac
• [x] PR code is formatted.
• [x] Allow edits from maintainers pull request option is set (recommended).

Additional context