🧪 Add tests for isinr and icosr scaling functions

[perim]

🎯 What: The testing gap addressed
This adds test coverage for the isinr and icosr scaling functions defined in direction.h, verifying that they correctly scale the base trigonometric functions relative to distance according to a standard float-based calculation.

📊 Coverage: What scenarios are now tested
The tests calculate results across all 16-bit angle inputs (from 0 to UINT16_MAX) and check for accuracy over a spectrum of distances ranging from 0 to 1,000,000. It asserts that deviations from actual float precision remain within calculated scaled tolerance limits based on known approximations in the integer trigonometric routines.

✨ Result: The improvement in test coverage
The isinr and icosr functions are now fully verified against a comprehensive matrix of angles and distances, assuring they retain correct scaling behavior. All changes were cleanly implemented and integrated into the existing test_direction.cpp suite which passes successfully under CTest.

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PR created automatically by Jules for task 18321200823291128918 started by @perim

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