Release GRASS GIS interface (r.flexure, v.flexure) with v2.0.0

[awickert]

The GRASS GIS addons r.flexure and v.flexure have been updated to be compatible with the gFlex v2.0.0 API and are ready to ship alongside the release.

The updated code lives on the update-flexure-modules branch of the grass-addons fork:
https://github.com/awickert/grass-addons/tree/update-flexure-modules

Relevant paths:

• grass7/raster/r.flexure/
• grass7/vector/v.flexure/

What was updated

• Removed PlateSolutionType (gone in v2; vWC1994 is the only stencil)
• Added support for pad_domain() via the -p flag on r.flexure
• Added sigma_xx, sigma_yy, sigma_xy in-plane stress options
• Fixed garray.array() usage for GRASS 8 compatibility
• Replaced grass.pygrass.vector with pure grass.script calls (ctypes incompatibility with conda Python)
• Rewrote HTML manuals; added EXAMPLES sections based on the gFlex RTD worked example
• Added grass.gunittest test suites (9 tests for r.flexure, 4 for v.flexure; all passing)

What remains before the PR to OSGeo/grass-addons

• Restore the >= 2.0.0 version guard (currently commented out with a TODO in both .py files)
• Add pip install gflex to the HTML install notes
• Review any additional v2.0.0 features worth exposing in the GRASS interface
• Open the PR against OSGeo/grass-addons

[awickert]

PRs open:
OSGeo/grass-addons#1744
OSGeo/grass-addons#1745