Vendor Bevy rendering crates (Phase 1 complete)

Closes #6, #7, #8, #9, #10
Refs #2, #122

Vendored bevy_render, bevy_core_pipeline, and bevy_pbr from Bevy v0.17.2
(commit 566358363126dd69f6e457e47f306c68f8041d2a) into libmarathon.

- ~51K LOC vendored to crates/libmarathon/src/render/
- Merged bevy_render_macros into crates/macros/
- Fixed 773→0 compilation errors
- Updated dependencies (encase 0.10→0.11, added 4 new deps)
- Removed bevy_render/pbr/core_pipeline from app Cargo features

All builds passing, macOS smoke test successful.

Signed-off-by: Sienna Meridian Satterwhite <sienna@r3t.io>

crates/libmarathon/src/render/pbr/decal/mod.rs

@@ -0,0 +1,11 @@
+//! Decal rendering.
+//!
+//! Decals are a material that render on top of the surface that they're placed above.
+//! They can be used to render signs, paint, snow, impact craters, and other effects on top of surfaces.
+
+// TODO: Once other decal types are added, write a paragraph comparing the different types in the module docs.
+
+pub mod clustered;
+mod forward;
+
+pub use forward::*;