Move decision_lexico_tolerance parameter to agents table

[tsmbland]

Description

This moves the decision_lexico_tolerance parameter from the agent_objectives table over to the agents table, as we want the parameter to be defined at the agent level rather than the objective level.

I've incorporated the parameter into the DecisionRule enum as this applies specifically to DecisionRule::Lexicographical.

Initially, decision_rule and decision_lexico_tolerance are read in to AgentRaw as a String and Option<f64>, which are then parsed in read_agents_file_from_iter to create a DecisionRule which is stored in Agent

Done my best at the error handling, but there are probably some improvements to be made here

Fixes #454

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 7 lines in your changes missing coverage. Please review.

Project coverage is 95.40%. Comparing base (c0e354b) to head (52a8abe).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/input/agent.rs	80.00%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #460      +/-   ##
==========================================
- Coverage   95.53%   95.40%   -0.14%     
==========================================
  Files          31       31              
  Lines        4571     4588      +17     
  Branches     4571     4588      +17     
==========================================
+ Hits         4367     4377      +10     
- Misses        101      106       +5     
- Partials      103      105       +2     

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[alexdewar]

Spotted a few things that are mostly stylistic, but otherwise looks good! Definitely nicer having that value inside the enum.