Remove deprecated std::iterator inheritance

[mjcarroll]

🦟 Bug fix

Fixes #505

Summary

Removes the use of the deprecated std::iterator template and replaces it with using the correct set of using statements.

I also added a gzEnum variadic template at clang's suggestion. This should probably be preferred over the macro where relevant.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[scpeters]

/github/workspace/src/EnumIface_TEST.cc:36:32: error: 'gzEnum' is not a member of 'gz::common'; did you mean 'gzEnum'?
     36 | auto myTypeIface = gz::common::gzEnum(
        |                                ^~~~~~
  In file included from /github/workspace/src/EnumIface_TEST.cc:20:
  /github/workspace/include/gz/common/EnumIface.hh:240:43: note: 'gzEnum' declared here
    240 | static constexpr gz::common::EnumIface<T> gzEnum(
        |                                           ^~~~~~

[codecov]

Codecov Report

Merging #529 (c35a188) into main (12872b3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head c35a188 differs from pull request most recent head 4d78133. Consider uploading reports for the commit 4d78133 to get more accurate results

@@           Coverage Diff           @@
##             main     #529   +/-   ##
=======================================
  Coverage   83.21%   83.22%           
=======================================
  Files          82       82           
  Lines        9880     9883    +3     
=======================================
+ Hits         8222     8225    +3     
  Misses       1658     1658           

Files	Coverage Δ
include/gz/common/EnumIface.hh	100.00% <100.00%> (ø)

[mjcarroll]

Windows failure was a flake here.