fix(mpc): use optimization result when polish failed

[TakaHoribe]

Description

Sometimes, the polish process in OSQP, which is designed to enhance result accuracy after optimization, can fail, particularly when the problem has a lot of constraints. However, in almost all cases, the optimization result meets the desired accuracy even if the polish fails. This PR allows the use of the optimization result even when the polish process is unsuccessful.

Before:

• Optimization failure -> publish stop command
• Polish failure (but optimization success) -> publish stop command

After:

• Optimization failure -> publish stop command
• Polish failure (but optimization success) -> keep using the optimization result

Tests performed

Not applicable.

Effects on system behavior

Not applicable.

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[TakaHoribe]

I can't believe why this test is running on EXPECT_FALSE.

[codecov]

Codecov Report

Patch coverage: 25.00% and no project coverage change.

Comparison is base (9dc104f) 14.89% compared to head (f1254db) 14.89%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4673   +/-   ##
=======================================
  Coverage   14.89%   14.89%           
=======================================
  Files        1549     1549           
  Lines      106942   106940    -2     
  Branches    32777    32776    -1     
=======================================
  Hits        15934    15934           
+ Misses      73617    73615    -2     
  Partials    17391    17391           

Flag	Coverage Δ		*Carryforward flag
differential	46.85% <25.00%> (?)
total	14.89% <ø> (-0.01%)	⬇️	Carriedforward from 9dc104f

*This pull request uses carry forward flags. Click here to find out more.

Files Changed	Coverage Δ
control/mpc_lateral_controller/test/test_mpc.cpp	51.31% <0.00%> (ø)
...ateral_controller/src/qp_solver/qp_solver_osqp.cpp	41.37% <33.33%> (+2.66%)	⬆️

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