BUG: Fix incorrect Jacobian in only_radial_burn branch of SolidMotor.evaluate_geometry

[Copilot]

The geometry_jacobian function in SolidMotor.evaluate_geometry had copy-paste errors in the only_radial_burn branch — the formulas were carried over from the non-radial burn case without adjustment, producing a mathematically wrong Jacobian that can degrade or derail LSODA integration.

Pull request type

• Code changes (bugfix, features)

Checklist

• CHANGELOG.md has been updated (if relevant)

Current behavior

For only_radial_burn, burn_area = 2π·r·h, so ṙ = −vdiff / (2π·r·h).

The Jacobian was incorrectly computed as:

• ∂ṙ/∂r = factor * (h − 2r) — copied from the non-radial case where d(burn_area)/dr = 2π(h−2r)
• ∂ṙ/∂h = 0 — wrong; height appears in the denominator so it has a non-zero partial

New behavior

Correct partial derivatives for burn_area = 2π·r·h:

# ṙ = -vdiff / (2π·r·h), factor = vdiff / (2π·(r·h)²)
inner_radius_derivative_wrt_inner_radius = factor * grain_height   # ∂ṙ/∂r = vdiff/(2π·r²·h)
inner_radius_derivative_wrt_height       = factor * grain_inner_radius  # ∂ṙ/∂h = vdiff/(2π·r·h²)
# dh/dt = 0, so height Jacobian row remains zero
height_derivative_wrt_inner_radius = 0
height_derivative_wrt_height       = 0

Breaking change

• No

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[Gui-FernandesBR]

Suggested change

	# dh/dt = 0, so all partial derivatives of height are zero
	# dh/dt = 0 (Height is a constant), so all partial derivatives of height are zero

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.09%. Comparing base (03f20c1) to head (4ad0554).
⚠️ Report is 5 commits behind head on rel/v1.12.0.

Files with missing lines	Patch %	Lines
rocketpy/motors/solid_motor.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           rel/v1.12.0     #944   +/-   ##
============================================
  Coverage        81.09%   81.09%           
============================================
  Files              107      107           
  Lines            13906    13906           
============================================
  Hits             11277    11277           
  Misses            2629     2629           

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