Upgrade bundled CLI11 to v2.6.2 and adapt integrations (validators, callbacks, extras, formatter)

[VolkerChristian]

Motivation

• Bring the in-tree CLI11 copy up to v2.6.2 to pick up bugfixes and new features and align the project with the newer API and behavior.
• Replace and simplify the previous custom formatter implementation and adapt the CLI integration to newer validator/callback/extras semantics.
• Add more robust handling for separators, RTTI detection, and more granular callback ordering to support richer subcommand/help behaviors.

Description

• Updated bundled header: bump CLI11 version macros to 2.6.2 and update copyright year.
• Introduced new feature flags and helpers: CLI11_HAS_RTTI, CLI11_MODULE_INLINE, get_group_separators(), and several small utility changes (e.g. binary_escape_string(force), process_quoted_string(...) overload).
• Validator and transform refactor: validators are now stored as shared_ptr<Validator>; added overloads to accept shared validators, transforms and function-based validators; reworked Validator combination operators and description merging.
• Callback orchestration: added CallbackPriority enum and phased _process_callbacks(...) to control ordering of callbacks and help/version triggers; updated help/version/help-all flags to use first-priority callbacks.
• Extras/config handling: replaced boolean allow_extras_ with ExtrasMode and allow_config_extras_ with ConfigExtrasMode, added PrefixCommandMode and improved _move_to_missing/extras handling and capture logic.
• Option and parsing improvements: added callback_priority to Option/OptionDefaults, support for non-standard short names, improved positional/parse fallthrough and prefix-matching support, refinements to result storage and lexical conversion handling.
• File/path validators and config parsing: added ExistingFile/Directory/Path/Nonexistent validators, split_program_name, check_path and related fixes for filesystem vs stat implementations.
• Formatter removal and CMake changes: removed the project-specific Formatter.h/Formatter.cpp and related usages, updated CMakeLists.txt to drop those sources and headers; adjusted code to use CLI11 built-in formatter behavior.
• SubCommand changes: adapted SubCommand to new CLI API (help flags, callback priorities), added requireCallback storage and runRequireCallbacks() integration invoked from config parsing flow.
• Various API and internal cleanups: enum underlying types, many small logic fixes (e.g. newline handling, joining, escaping, option naming and joining behavior) across the header and calling code.

Testing

• Project built with CMake (reconfigured to drop removed formatter sources) and compiled successfully (utils target and overall project build completed).
• Ran project's automated unit/integration tests (test suite) after the change and observed the test run completed without failures.
• Executed core command-line flows exercised by SubCommand/config parsing paths (help/version, config write/read, flag parsing) to validate behavior; observed expected help/version outputs and config handling.

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Codex Task