BUG: seed Monte Carlo per simulation index, not per worker (#1053)

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Pull request type

• Code changes (bugfix, features)

Checklist

• Tests for the changes have been added
• Lint passes locally (ruff check and ruff format --check; pylint 10/10 on the touched files)
• Affected unit suites pass locally (test_monte_carlo.py, tests/unit/stochastic); relying on CI for the full slow suite
• CHANGELOG.md updated

Current behavior

MonteCarlo.simulate() seeds the stochastic models per worker in parallel mode and effectively once at construction in serial mode, so the inputs a given simulation index receives depend on how the run was executed rather than on the index. Parallel spawns one seed per worker from a fresh unseeded SeedSequence, and each worker draws for whatever sims it pulls off the shared counter; serial draws one long sequential stream. Result: serial, n_workers=2, and n_workers=4 all sample different inputs, and parallel runs aren't reproducible run to run. This is #1053.

New behavior

Each simulation's seed is derived from (master seed, simulation index) via SeedSequence, reseeding the models before every simulation in both paths. Adds an optional seed to MonteCarlo; the master entropy is captured once, so seed=None stays random but consistent across execution modes within a run. A given index now samples identical inputs regardless of serial/parallel or n_workers, and a fixed seed reproduces a whole run. Integer child seeds (not SeedSequence objects) keep custom samplers' reset_seed working.

Breaking change

• No

With seed=None the sampling is unchanged in spirit (still random), but numeric samples for existing unseeded runs will differ, since seeding is now per-index rather than one sequential stream. The seed argument is opt-in.

Additional information

Adds test_seed_makes_inputs_reproducible_by_index and test_unseeded_monte_carlo_is_index_consistent in tests/unit/simulation/test_monte_carlo.py.

Closes #1053

[Gui-FernandesBR]

duplicated with #1053

[codecov]

Codecov Report

❌ Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.22%. Comparing base (ce3342f) to head (a0b9536).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
rocketpy/simulation/monte_carlo.py	76.92%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1071      +/-   ##
===========================================
+ Coverage    80.85%   82.22%   +1.37%     
===========================================
  Files          122      122              
  Lines        16355    16361       +6     
===========================================
+ Hits         13224    13453     +229     
+ Misses        3131     2908     -223     

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