Remove ``using namespace nda" to Avoid Namespace Pollution

[yangyu1412]

Description:

Some header files use using namespace nda. Including these headers in a project can lead to unintended consequences, such as misrecognition of functions in other external libraries as belonging to the nda namespace, which results in compilation errors.

Changes:

• Removed using namespace nda from header files.
• Explicitly added nda:: namespace qualification where necessary in the affected code.

Notes:

• I am currently submitting this PR against the release branch; however, it might be more appropriate to also merge this change into the development branch, but I haven't checked what is in the development branch.
• If there are alternative suggestions to address this issue without removing using namespace nda, I'm happy to learn.