Simplify reduce_wheel_speed_until_steering_reached logic (backport #2396)

[mergify]

Description

While checking #2392 I was confused by the code. I used the chance to simplify the logic a bit.

Is this user-facing behavior change?

Minimal, the scale is continuous now as cos(max_phi_delta) / cos(min_phi_delta) is not exactly 0.01.

Did you use Generative AI?

no

Additional Information

---

This is an automatic backport of pull request #2396 done by [Mergify](https://mergify.com).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.13%. Comparing base (4ab9822) to head (33ce5f6).

Additional details and impacted files

@@            Coverage Diff             @@
##            jazzy    #2427      +/-   ##
==========================================
- Coverage   86.13%   86.13%   -0.01%     
==========================================
  Files         158      158              
  Lines       15865    15864       -1     
  Branches     1393     1393              
==========================================
- Hits        13665    13664       -1     
+ Misses       1700     1699       -1     
- Partials      500      501       +1     

Flag	Coverage Δ
unittests	86.13% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ng_controllers_library/src/steering_kinematics.cpp	83.33% <100.00%> (-0.10%)	⬇️

... and 1 file with indirect coverage changes

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