refactor: rename cortex-neuron binary and crate to neuron

Package name, lib name, and binary all now just "neuron" without
the cortex- prefix.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/neuron/Cargo.toml

@@ -1,15 +1,15 @@
 [package]
-name = "cortex-neuron"
+name = "neuron"
 version.workspace = true
 edition.workspace = true
 license.workspace = true
 
 [lib]
-name = "cortex_neuron"
+name = "neuron"
 path = "src/lib.rs"
 
 [[bin]]
-name = "cortex-neuron"
+name = "neuron"
 path = "src/main.rs"
 
 [dependencies]