Various updates: least squares orbit solves, specular bug fix, packaging bug fix

[ryanketzner]

Adds generalized least-squares differential correction for estimating spacecraft drag and initial state parameters using CYGNSS trajectory data. Orekit propagation now supports explicitly requested output epochs (needed for least squares solve) while retaining the existing propagation time based interface, project dependencies and packaging are corrected, and CoverageKinematics is updated with bug fix that was causing error in specular point code.

Added:

• examples/cygnss_data/cygnss_spacecraft_trajectory_combined.csv: Three-day CYGNSS reference trajectory data.
• examples/solve_drag_coefficient.py: An example that retrieves a CYGNSS initial orbit from spacetrack, estimates its drag coefficient against reference positions, and plots residuals and solver convergence. This solves for a negative drag coefficient, presumably due to velocity error in CYGNSS data.
  examples/solve_drag_coefficient_x0.py: An example that jointly estimates the drag coefficient and initial Cartesian state using the first half of the reference arc, then evaluates the solution across the full trajectory.
• orbitpy/glsdc.py: A module for generalized nonlinear least-squares differential-correction supporting weighted residuals, parameter scaling, and analytical or central finite-difference Jacobians.

Modified:

• environment.yml: Adds Orekit to the Conda environment dependencies (was previously missing when it should have been there).
• extern/CoverageKinematics: Advances the submodule to add coverage-runtime comparison examples and fix a race condition in LOSEventSource by making its ray and intersection-query state local to each update.
• orbitpy/orekitpropagator.py: Adds execute_2 for propagation at explicitly supplied epochs (needed for least squares solve). The existing execute method now constructs its regular time grid and delegates to the new method for backward compatibility.
• pyproject.toml: Adds Orekit as a runtime dependency and corrects the wheel package path from src/orbitpy to orbitpy.