Resolve "Add more profiling regions in Maxwell code"

Add more profiling regions to identify bottlenecks in initialization.

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Add here a one line description to be included in the Changes page. You can delete this section if the changes are trivial and of no consequence for the users.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

Closes #418 (closed)