fix: avoid wrong upshift and downshift for light SMT vehicles

• Add condition to delay downshift in SMT while braking with negative gradient low speed
  • to avoid brake case with positive gradient where distance cannot be achieved
  • condition is very selective to forbid downshifting only when braking uphill if reengage below disengage speed (no consumption delta observed on multiple cases tests)
  • if used in positive torque or with negative gradient, the consumption drops due to extensive use of high gear ratio
• Aux Mechanical Power not negligible for small vehicles, included in computation of:
  • start reserve (change of defnintion in AMT and SMT)
  • clutch slipping speed (in Clutch)
• Add a condition to upshift when max speed is exceeded (SMT only): (the upshift should not results in an immediate downshift)
  • considering Speed drop for SMT due to long shift time that generated issues on #758

Test performed on all art10 issue files from #176 to #845 - no change of consumption on AMT vehicles (max 0.01%) - reduction of consumption on SMT buses - from 0.01% on Interurban to max 3.5% on HeavyUrban for SMT vehicles, - due mostly to better starts matching target acceleration and less shifting than a change in energy to provide to the wheel (eg. positive wheel energy variation on #420 HeavyUrban: -0.02%) - issues solved: #750, #758, #769, #816, #821, #829