Reworked Configuration Namelist Access API

[mo-rickywong]

PR Summary

Sci/Tech Reviewer: @allynt
Code Reviewer: @MatthewHambley

This PR is to allow users more direct access to the namelist configuration values from
Fortran object (rather than global module scope) while maintaining it's read-only nature.
e.g.
modeldb%config%<MyNamelist>%MyNamelistMember()

This PR is linked to LFRic-core trac ticket #4702, which provides more details on the change itself

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trac.log

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[MatthewHambley]

I notice that across the board you assign namelist values to variables before using them. Can you confirm this is a choice you've made and that, as functions, they can be used in-line. e.g. call something(value, modeldb%config%my_namelist%other_value().

Yes this is a choice, the values can be accessed in-line. I have extracted them as the variables existed and shortens the actual code so it appears cleaner.

[MatthewHambley]

Not too many changes, some of which may be postponed to later sets.

[MatthewHambley]

There's still much to be done to tidy things up but this gets the basic functionality in place.

[mike-hobson]

From a code owner's point of view, this seems fine.

[allynt]

I'd agree w/ @MatthewHambley, having synchronised lists to track whether namelist n allows duplicates seems a bit fragile. A list of objects might be more robust. And, the @dataclass decorator makes creating an object much easier. Something like:

@dataclass
class NamelistDetails:
  name: str
  duplicate: Optional[bool] = False

class AppConfiguration:
  def __init__(self, module_name: str):
    ...
    self._namelist_details: List[NamelistDetails] = []
    ...

   def add_namelist(self, name: str, duplicate: bool) -> None:
     ...
     self._namelist_details.append(NamelistDetails(name, duplicate))
    ...

But that would require a big chunk of rewriting, so perhaps create a new issue? (I'm willing to do the work).

[mo-rickywong]

I agree it's not the best and is definitely fragile. Though in defence, most users will not be running this manually from the command line. The input is determined from the json file that is generated from rose_picker (or other application).

This PR is definitely an iteration to get the new api up and running, I've create issue #260 for this and assigned it to @allynt as requested

[allynt]

LGTM