feat: separate ThermoParams/GridParams for v0.3.0

[MasanoriKanamaru]

Summary

• Extract GridParams from the monolithic ThermoParams so that thermophysical material properties and numerical grid configuration are held in separate, focused types
• Add keyword-argument constructors for both types and a mixed scalar/vector constructor for ThermoParams
• Update all problem constructors, solvers, and tests to the new API

Changes

New type: GridParams

# Keyword constructor (recommended) — Δz is auto-computed
grid_params = GridParams(; z_max=0.6, n_depth=61)

# Positional constructor — explicit Δz (advanced use)
grid_params = GridParams(z_max, n_depth, Δz)

Fields: z_max, n_depth, Δz (primary params first, derived last).

Redesigned ThermoParams

# Keyword constructor (recommended)
thermo_params = ThermoParams(
    conductivity    = 0.1,
    density         = 1270.0,
    heat_capacity   = 600.0,
    reflectance_vis = 0.04,
    reflectance_ir  = 0.0,
    emissivity      = 1.0,
)

# Mixed scalar/vector — scalars are auto-broadcast to match vector length
thermo_params = ThermoParams(
    conductivity    = [0.1, 0.3, ...],  # per-face vector
    density         = 1270.0,           # scalar → broadcast
    heat_capacity   = 600.0,
    reflectance_vis = [0.04, 0.1, ...],
    reflectance_ir  = 0.0,
    emissivity      = 1.0,
)

Updated problem constructors

# Single asteroid
problem = SingleAsteroidThermoPhysicalProblem(shape, thermo_params, grid_params; ...)

# Binary asteroid — per-body or shared params
problem = BinaryAsteroidThermoPhysicalProblem(
    (shape1, shape2),
    (thermo_params1, thermo_params2),
    (grid_params1, grid_params2);
    ...
)
# shared:
problem = BinaryAsteroidThermoPhysicalProblem(
    (shape1, shape2), thermo_params, grid_params; ...
)

Breaking Changes

Before (v0.2.x)	After (v0.3.0)
ThermoParams(k, ρ, Cₚ, R_vis, R_ir, ε, z_max, Δz, n_depth)	ThermoParams(…) + GridParams(; z_max, n_depth)
thermo_params.thermal_conductivity	thermo_params.conductivity
thermo_params.n_depth / .Δz	grid_params.n_depth / .Δz
Problem(shape, thermo_params; …)	Problem(shape, thermo_params, grid_params; …)
broadcast_thermo_params!	removed (expansion happens at construction time)

Test plan

• Unit tests for ThermoParams: scalar, keyword, vector, mixed scalar/vector, keyword mixed, mismatched-length validation (test/test_thermo_grid_params.jl)
• Unit tests for GridParams: keyword auto-Δz, positional explicit Δz, constructor consistency
• All existing integration tests updated and passing (Pkg.test() — 189 tests, 0 failures)
• Migration guide added to CHANGELOG.md

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.75%. Comparing base (b599cc1) to head (ddc9258).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #218      +/-   ##
==========================================
+ Coverage   96.59%   96.75%   +0.16%     
==========================================
  Files          14       15       +1     
  Lines         704      709       +5     
==========================================
+ Hits          680      686       +6     
+ Misses         24       23       -1     

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