fix: complete partial temperature ramps

[galjos]

Closes #341.

• compute ramp increments from the actual scheduled updates
• validate empty ramps and zero update frequencies before thermostat state changes
• exercise the behavior through input parsing

Tests:

• testThermostatSetup

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.83%. Comparing base (109a355) to head (bac53cc).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #351   +/-   ##
=======================================
  Coverage   89.83%   89.83%           
=======================================
  Files         291      291           
  Lines       11535    11543    +8     
  Branches     3601     3606    +5     
=======================================
+ Hits        10362    10370    +8     
  Misses       1131     1131           
  Partials       42       42           

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[pq-perf-bot]

⚡ Performance (instruction count) — ✅ no regressions

per-benchmark breakdown

benchmark	base Ir	PR Ir	Δ
bondedForces	41.47M	41.47M	-0.00%	✅
boxTransforms	10.67M	10.67M	+0.00%	✅
constraints	11.41M	11.41M	+0.00%	✅
coulombKernel	5.80M	5.80M	+0.00%	✅
forceKernel	15.35M	15.35M	+0.00%	✅
integrator	32.19M	32.19M	+0.00%	✅
kinetics	9.53M	9.53M	+0.00%	✅
linearAlgebra	2.07M	2.07M	+0.00%	✅
nonCoulombPairs	5.48M	5.48M	+0.00%	✅
shiftVector	5.81M	5.81M	+0.00%	✅
virial	11.64M	11.64M	-0.07%	✅

_{Deterministic callgrind instruction counts vs the base branch; gated at ±2%. Not wall-clock.}

[ape33]

see comment, otherwise approved

[ape33]

please also update the formatting of this comment