Sfsimodels

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* Fixed surface meshing issue
* Added `loop` to TwoDSystem for length out-of-plane.

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* Added new `get_nearest_node_index_at_x` to ortho mesh.

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* Soil now defines water mass density `wmd` and `liq_sg` instead of `liq_mass_density` to allow for not water liquids.
* Can retrieve the `unique_hash` from the ecp file for each object under the `loaded_unique_hash` parameter.
* Allow soil liquid mass to be changed.
* When loading an ecp file the loader does not fail when trying to set a non-settable attribute, instead it just does not set the attribute
* Fixed issue with meshing when adjusting for a smooth slope, when slope was going down to the right the top slope could be slightly wrong
* Improved meshing 2d vary xy - when multiple adjacent sloping surfaces on surface

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* Improved saving and loading of `TwoDSystem`
* Allowed calculation of effective stress when soil under water and dry weight is not set
* Fixed issue where soil_profile.move_layer function would delete layer if new position was equal to previous position
* Fixed issue with mesh vary2DXY where mesh could not adjust near the surface
* Fixed issue with mesh vary2DY and vary2DXY when trimming mesh, where it could create a deformity
* Added `ip_axis` to foundation default outputs (`ip_axis` is in-plane axis)
* When using the `set_section_prop` on a `BeamColumnElement` the property is automatically added to the outputs list
* Can load `Material` object into `Building` as `Building.material`
* Can load `Material` object into `Section` as `Section.material` or `Section.mat`
* Added `sm.std.create_rc_beam()` function to create an RC beam element with RC sections.
* Added `override` option to the `Foundation` object to override pre-computed properties.

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* Added in plane axis (`ip_axis`) and out-of-plane axis (`oop_axis`) parameters for foundation.
* Added new constructor to `sfsimodels.num.mesh` `FiniteElementVary2DMeshConstructor`,
which constructs either `FiniteElementVaryY2DMesh` where x-coordinates remain unchanged with depth,
but y-coordinates vary with x-distance, or `FiniteElementVaryXY2DMesh` where both x- and y-coordinates vary
throughout the mesh.

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* Improved handling of sections and materials
* Added `get_oop_axis` method to foundations to get the out-of-plane axis
* PadFoundation can now handle irregular spacing of footings
* Meshing can handle foundation out-of-plane input