Static initialization

[K20shores]

This replaces the validation keys struct in both v0 and v1 with static constexpr const char* variables for keys.

When using std::string, we were running into a static initialization problem (also see the linked article in the answer for more detail). This apparently isn't a problem within the library, but attempting to use those values in the musica performance repo caused this issue to pop up here and in micm.

[Copilot]

Pull Request Overview

This PR refactors the key validation mechanism by replacing the old keys struct with static constexpr const char* variables for keys, and updates all parser files (both v0 and v1) to use the new syntax.

• Replaces old brace-initialized key structures with std::vectorstd::string initializations using static constexpr key variables.
• Updates all usage of validation::keys. to validation:: in parser files.
• Revises header files in v0 and v1 to reflect the new key definitions.

Reviewed Changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/v1/emission_parser.cpp	Updates key references to use static constexpr variables.
src/v1/condensed_phase_photolysis_parser.cpp	Updates key references and vector initializations.
src/v1/condensed_phase_arrhenius_parser.cpp	Refactors key usage and error message updates for mutually exclusive options.
src/v1/branched_parser.cpp	Replaces old key syntax with new static constexpr key variable usage.
src/v1/arrhenius_parser.cpp	Consistent update of Arrhenius key references using new definitions.
src/v1/aqueous_equilibrium_parser.cpp	Refactors key references and vector initialization.
(v0 files)	All parser files updated uniformly replacing key struct access.
include/mechanism_configuration/v1/validation.hpp	Removes the keys struct and defines keys as static constexpr variables.
include/mechanism_configuration/v0/validation.hpp	Updates key definitions to use static constexpr const char*.

[mattldawson]

nice!