Splits the large src/tests.rs into smaller tests

[grenewode]

Splits tests out of the monolithic test file, into smaller and more easily understood individual files.

This is an ongoing project, but I think there could be enough here to be worth merging.

[recurseml]

Review by RecurseML

🔍 Review performed on aa9c78e..b92c738

✨ No bugs found, your code is sparkling clean

✅ Files analyzed, no issues (34)

• Cargo.lock
• Cargo.toml
• src/io/dxf.rs
• src/io/obj.rs
• src/io/stl.rs
• src/lib.rs
• src/main.rs
• src/mesh/bsp.rs
• src/mesh/flatten_slice.rs
• src/mesh/mod.rs
• src/mesh/plane.rs
• src/mesh/polygon.rs
• src/mesh/shapes.rs
• src/mesh/smoothing.rs
• src/mesh/vertex/interpolation_methods.rs
• src/mesh/vertex/mod.rs
• src/mesh/vertex/vertex_cluster.rs
• src/sketch/extrudes.rs
• src/sketch/shapes.rs
• src/tests.rs
• tests/bug_tests.rs
• tests/csg_tests.rs
• tests/feature_chull_io_tests.rs
• tests/feature_offset_tests.rs
• tests/feature_stl_io_tests.rs
• tests/feature_truetype_text_tests.rs
• tests/mesh_tests.rs
• tests/metadata_tests.rs
• tests/misc_tests.rs
• tests/node_and_clipping_tests.rs
• tests/node_tests.rs
• tests/plane_tests.rs
• tests/polygon_tests.rs
• tests/support/mod.rs