client/container: root: refactor common namespace

- Factor out respective common from macro and apply to all scopes
  * `dfi::common`
  * `dfi::macro::common`
  * `dfi::plugin::common`

- Add deprecation warnings in `dfi::macro::common`
  * Common functionality (not macro specific) is now in `dfi::common`

- Add convenience wrappers to inner common impl, where appropriate
  * Allows for backwards compatibility

- Add/update/clarify code docs and Doxygen definitions

- Related refactoring

NOTE: all changes are backward compatible (no need to bump major).

client/Doxygen/docker-finance.dox

@@ -1,6 +1,6 @@
 // docker-finance | modern accounting for the power-user
 //
-// Copyright (C) 2021-2024 Aaron Fiore (Founder, Evergreen Crypto LLC)
+// Copyright (C) 2021-2025 Aaron Fiore (Founder, Evergreen Crypto LLC)
 //
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
@@ -100,6 +100,10 @@
 //! \brief Group for testing framework (benchmarks, unit testing)
 //! \since docker-finance 1.0.0
 
+//! \defgroup cpp_common_impl docker-finance C++ shared common code
+//! \brief Group for common functionality (internal and external)
+//! \since docker-finance 1.1.0
+
 //
 // PHP
 //