feat: add MM Hessian workflow

[galjos]

Adds the mm-hessian workflow with optional pre-optimization, finite-difference Hessian builders, metadata output, tests, examples, and documentation.

Closes #276
Related: MolarVerse/PQAnalysis#150

[pq-perf-bot]

⚡ Performance (instruction count) — ✅ no regressions

per-benchmark breakdown

benchmark	base Ir	PR Ir	Δ
bondedForces	41.46M	41.46M	+0.00%	✅
boxTransforms	10.67M	10.67M	+0.00%	✅
constraints	11.38M	11.38M	+0.00%	✅
coulombKernel	5.80M	5.80M	+0.00%	✅
forceKernel	15.33M	15.33M	+0.00%	✅
integrator	32.17M	32.17M	+0.00%	✅
kinetics	9.53M	9.53M	+0.00%	✅
linearAlgebra	2.08M	2.08M	+0.00%	✅
nonCoulombPairs	5.48M	5.48M	-0.00%	✅
shiftVector	5.81M	5.81M	+0.01%	✅
virial	11.63M	11.63M	+0.00%	✅

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

[codecov]

Codecov Report

❌ Patch coverage is 89.87854% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.56%. Comparing base (524c613) to head (8e603ff).

Files with missing lines	Patch %	Lines
src/settings/hessianSettings.cpp	79.06%	9 Missing ⚠️
src/setup/outputFilesSetup.cpp	28.57%	4 Missing and 1 partial ⚠️
src/input/inputFileParser/hessianInputParser.cpp	91.48%	4 Missing ⚠️
src/opt/evaluator/evaluator.cpp	20.00%	4 Missing ⚠️
src/settings/settings.cpp	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #277      +/-   ##
==========================================
- Coverage   89.57%   89.56%   -0.02%     
==========================================
  Files         289      293       +4     
  Lines       11149    11387     +238     
  Branches     3466     3572     +106     
==========================================
+ Hits         9987    10199     +212     
- Misses       1122     1147      +25     
- Partials       40       41       +1     

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