refactor: standardize cost model JSON formatting to 4-space indentation

Reformat builtin cost model JSON files to use consistent 4-space
indentation instead of 2-space indentation. This improves readability
and aligns with common JSON formatting conventions for configuration
files.

No semantic changes - only whitespace formatting updated.

Files affected:
- builtinCostModelA.json
- builtinCostModelB.json
- builtinCostModelC.json

Author: Unisay