Simplify CLib's (Shared)Cabinet

[ischoegl]

Changes proposed in this pull request

This PR is mostly house-keeping for a simple bulk-replacement to streamline CLib's storage class (a left-over item from #1770 which I decided to break down into more manageable chunks)

• Replace all occurrences of SharedCabinet::item by SharedCabinet::at
• Replace all occurrences of SharedCabinet::get by SharedCabinet::as`
• Eliminate SharedCabinet::item and SharedCabinet::get
• Rename SharedCabinet back to Cabinet (original name of before shared pointers were introduced in #1448)

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] Build passes (scons build & scons test) and unit tests address code coverage
• [x] Style & formatting of contributed code follows contributing guidelines
• [x] The pull request is ready for review

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 19.87041% with 371 lines in your changes missing coverage. Please review.

Project coverage is 73.20%. Comparing base (74c971d) to head (08c9ee6). Report is 3 commits behind head on main.

Files	Patch %	Lines
src/clib/ct.cpp	24.55%	169 Missing :warning:
src/clib/ctonedim.cpp	26.92%	57 Missing :warning:
src/clib/ctmultiphase.cpp	1.78%	55 Missing :warning:
src/clib/ctreactor.cpp	7.14%	52 Missing :warning:
src/clib/ctrpath.cpp	0.00%	24 Missing :warning:
src/clib/ctsurf.cpp	0.00%	8 Missing :warning:
src/clib/Cabinet.h	50.00%	5 Missing :warning:
src/clib/ctfunc.cpp	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1780 +/- ## ======================================= Coverage 73.20% 73.20% ======================================= Files 381 381 Lines 54244 54240 -4 Branches 9237 9236 -1 ======================================= - Hits 39709 39707 -2 Misses 11564 11564 + Partials 2971 2969 -2 ```

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[ischoegl]

This makes sense to me, @ischoegl. Just one minor suggestion.

Thanks for the prompt review, @speth! I adopted your suggestion.