Add a class that implements Euler Inversion for source location (#660)

The `EulerInversion` class implements the method, which is much less
sensitive to noise in the data and interfering sources. It can estimate
the integer structural index as well, though a known value can also be
given. The class only implements fitting data in a single window (moving
window approaches will come later). The initial estimate for the
non-linear process is the Euler Deconvolution result.

Author: leouieda

doc/api/index.rst

@@ -117,6 +117,7 @@ Source position estimation
 .. autosummary::
     :toctree: generated/
 
+    EulerInversion
     EulerDeconvolution
 
 

doc/references.rst

@@ -26,6 +26,7 @@ References
 .. [Soler2021] Soler, S. R. and Uieda, L. (2021). Gradient-boosted equivalent sources, Geophysical Journal International. doi:`10.1093/gji/ggab297 <https://doi.org/10.1093/gji/ggab297>`__
 .. [Uieda2014] Uieda, L., V. C. Oliveira Jr., and V. C. F. Barbosa (2014), Geophysical tutorial: Euler deconvolution of potential-field data, The Leading Edge, 33(4), 448-450, doi:`10.1190/tle33040448.1 <https://doi.org/10.1190/tle33040448.1>`__.
 .. [Uieda2015] Uieda, Leonardo (2015). A tesserioid (spherical prism) in a geocentric coordinate system with a local-North-oriented coordinate system. figshare. Figure. doi: `10.6084/m9.figshare.1495525.v1 <https://doi.org/10.6084/m9.figshare.1495525.v1>`_
+.. [Uieda2025] Uieda, L., Souza-Junior, G. F., Uppal, I., Oliveira Jr., V. C. (2025). Euler inversion: Locating sources of potential-field data through inversion of Euler's homogeneity equation. Geophysical Journal International. doi:`10.1093/gji/ggaf114 <https://doi.org/10.1093/gji/ggaf114>`__.
 .. [Vajda2004] Vajda, P., Vaníček, P., Novák, P. and Meurers, B. (2004). On evaluation of Newton integrals in geodetic coordinates: Exact formulation and spherical approximation. Contributions to Geophysics and Geodesy, 34(4), 289-314.
 .. [Takahashi2018] Takahashi, D., Oliveira Jr., V. C., & Barbosa, V. C. F. (2020). Convolutional equivalent layer for gravity data processing. GEOPHYSICS, 85(6), G129–G141. https://doi.org/10.1190/geo2019-0826.1
 .. [TurcotteSchubert2014] Turcotte, D. L., & Schubert, G. (2014). Geodynamics (3 edition). Cambridge, United Kingdom: Cambridge University Press.

src/harmonica/__init__.py

@@ -14,7 +14,7 @@
 from ._equivalent_sources.cartesian import EquivalentSources
 from ._equivalent_sources.gradient_boosted import EquivalentSourcesGB
 from ._equivalent_sources.spherical import EquivalentSourcesSph
-from ._euler_deconvolution import EulerDeconvolution
+from ._euler_methods import EulerDeconvolution, EulerInversion
 from ._forward.dipole import dipole_magnetic
 from ._forward.ellipsoids import Ellipsoid, ellipsoid_gravity, ellipsoid_magnetic
 from ._forward.point import point_gravity