[HOLD] Adapt solutions to new initial-guess grids

[mickaelbegon]

What changed

• add Solution.to_initial_guesses(...)
• add public adapt_solution_to_initial_guesses(...)
• resample states, controls and algebraic variables onto target shooting or collocation grids
• transfer parameters without relying on InitialGuessList.values() or private attributes
• preserve constant, linear, each-frame and all-points interpolation semantics

Why

Warm starts between windows or solvers need a supported way to adapt solutions when node counts and transcription grids differ.

Validation

• pytest -q tests/shard4/test_solution_grid_adaptation.py
• 2 passed

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This change is