feat: add MM Hessian workflow

[galjos]

Summary

• add mm-hessian job type with optional pre-optimization
• add finite-difference Hessian builders and metadata output
• add parser/settings/Hessian-builder tests, example inputs, docs, and changelog fragment

Closes #276
Related: MolarVerse/PQAnalysis#146

Checks

• cmake --build /tmp/pq-mm-hessian-pr-build -j 8
• ctest --test-dir /tmp/pq-mm-hessian-pr-build -R "test(HessianBuilder|GeneralParser|HessianParser|HessianSettings|InputFileReader|TimingsParser)$" --output-on-failure
• ctest --test-dir /tmp/pq-mm-hessian-pr-build -E "testBruteForceCellListEquivalence$" --output-on-failure
• python -m sphinx -b html docs/sphinx /tmp/pq-docs-pr-check

Note: unfiltered ctest is 143/144; testBruteForceCellListEquivalence segfaults outside this diff and also fails alone.

[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 89.06883% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.13%. Comparing base (1d02915) to head (00b79fe).

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 ⚠️
src/settings/timingsSettings.cpp	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #277      +/-   ##
==========================================
+ Coverage   88.12%   88.13%   +0.01%     
==========================================
  Files         283      287       +4     
  Lines       10874    11112     +238     
  Branches     3376     3482     +106     
==========================================
+ Hits         9583     9794     +211     
- Misses       1251     1277      +26     
- Partials       40       41       +1     

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