Make fmt, std::format optional

[K20shores]

Introduces a CMake option (default OFF) to use the {fmt} library instead of std::format, A shim header (format_compat.hpp) aliases fmt or std into mc_fmt so call sites are unchanged. Packaging conditionally installs fmt when built from source and emits find_dependency(fmt) when found via the system.

This change is necessary because NOAA uses GCC11 which does not have full c++ 20 support and they can't use std::format. We will reject this PR if they can get their compiler stack updated to a supported version of GCC

Also removed some unused variables and some erronoues std::move

closes #262

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.00%. Comparing base (b5730b0) to head (a18a8d9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #263   +/-   ##
=======================================
  Coverage   70.00%   70.00%           
=======================================
  Files           5        5           
  Lines          10       10           
=======================================
  Hits            7        7           
  Misses          3        3           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

Adds an opt-in build path to support C++17 by routing formatting calls through a compatibility shim that uses either {fmt} or std::format, and updates CMake/packaging to conditionally bring in {fmt}.

Changes:

• Introduce MECH_CONFIG_USE_FMT (default OFF) to build with C++17 + {fmt} instead of C++20 + std::format.
• Add format_compat.hpp shim and migrate call sites from std::format(...) to mc_fmt::format(...).
• Update packaging/config generation to optionally install/declare {fmt} as a dependency; adjust ErrorLocation formatter specialization and NodeInfo construction for C++17 compatibility.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/validate_schema.cpp	Switch formatting calls to mc_fmt::format via shim include.
src/parser.cpp	Replace std::format usage with mc_fmt::format.
src/development/utils.cpp	Replace std::format usage with mc_fmt::format.
src/development/type_validators.cpp	Replace std::format usage with mc_fmt::format.
src/development/reactions/validators/wet_deposition.cpp	Replace <format> include with shim include.
src/development/reactions/validators/user_defined.cpp	Replace <format> include with shim include.
src/development/reactions/validators/taylor_series.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/surface.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/simpol_phase_transfer.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/photolysis.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/lambda_rate_constant.cpp	Replace <format> include with shim include.
src/development/reactions/validators/henrys_law.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/first_order_loss.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/emission.cpp	Replace <format> include with shim include.
src/development/reactions/validators/condensed_phase_photolysis.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/condensed_phase_arrhenius.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/branched.cpp	Replace <format> include with shim include.
src/development/reactions/validators/arrhenius.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/development/reactions/validators/aqueous_equilibrium.cpp	Replace <format> include with shim include.
src/development/models/validators/modal.cpp	Replace formatting calls with mc_fmt::format.
src/development/mechanism.cpp	Replace formatting calls with mc_fmt::format and include shim.
src/CMakeLists.txt	Conditionally set C++17 + {fmt} vs C++20 + std::format.
packaging/CMakeLists.txt	Conditionally install/export {fmt} target and set config-time dependency flag.
include/mechanism_configuration/format_compat.hpp	New shim header selecting {fmt} or std::format under mc_fmt.
include/mechanism_configuration/error_location.hpp	Use shim include and provide {fmt} vs std::formatter specialization.
include/mechanism_configuration/development/utils.hpp	Add NodeInfo constructor to support C++17 (non-parenthesized aggregate init).
cmake/mechanism_configurationConfig.cmake.in	Conditionally find_dependency(fmt) for consumers.
cmake/dependencies.cmake	Add optional {fmt} FetchContent dependency when enabled.
CMakeLists.txt	Add MECH_CONFIG_USE_FMT option; remove global C++20 standard setting.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.