Create agent_cost_limits table

[tsmbland]

Description

Splitting cost limits out from the main agents table so they can be specified by year

Fixes #455

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 95.86207% with 6 lines in your changes missing coverage. Please review.

Project coverage is 94.54%. Comparing base (d502c32) to head (f43e5cb).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
src/input/agent/cost_limit.rs	97.03%	0 Missing and 4 partials ⚠️
src/input/agent.rs	66.66%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #499      +/-   ##
==========================================
+ Coverage   94.33%   94.54%   +0.20%     
==========================================
  Files          37       38       +1     
  Lines        4751     4878     +127     
  Branches     4751     4878     +127     
==========================================
+ Hits         4482     4612     +130     
+ Misses        138      128      -10     
- Partials      131      138       +7     

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[tsmbland]

Converted back to draft as this needs to be updated to use parse_year_str instead of YearSelection

[tsmbland]

Ok ready now (once #475 is approved)

[alexdewar]

LGTM!

[alexdewar]

Suggested change

	let milestone_years = vec![2020, 2025];
	let iter = vec![create_agent_cost_limits_raw(
	let milestone_years = [2020, 2025];
	let iter = [create_agent_cost_limits_raw(

[alexdewar]

For iterators with one thing in you can also just use std::iter::once