Add `photolysis_calculator:` configuration

See #268. Add PhotolysisCalculator struct to mechanism_configuration:: and parsing logic to the v1 parser.

Acceptance criteria

• std::optional<PhotolysisCalculator> photolysis_calculator added to Mechanism
  • likely only needs to provide a filepath
  • we can check that the filepath exists
    • however for tuv, it's configuration file might need to be specified as a relative path, which means the existance check might not be helpful or feasible
  • this would also support cloud j, which we might be adding support for

Ideas

• If we do a path existence check, it belongs in validate(), not `parse()

Start by reading the context in #268 and locating the Mechanism type in the mechanism_configuration namespace, then trace the v1 parser and validate() flow. Add the optional PhotolysisCalculator configuration with its filepath and parsing support, resolving whether validation should check path existence; done means the v1 configuration parses and the acceptance criteria are covered.