build(uci): enable vendored UCI builds and Unix development support

Switch rust-uci dependency to the Lochnair fork with vendored UCI
feature for self-contained builds without system libuci. Add
uci-vendored feature flag (enabled by default) that pulls in the
vendored C library. UCI support on non-Linux Unix is intended for
development and testing.

Cargo.toml

@@ -38,9 +38,10 @@ netlink-bindings = { version = "0.3.3", features = ["rt-link", "tc"] }
 netlink-socket2 = { version = "0.3.3" }
 
 [target.'cfg(unix)'.dependencies]
-rust-uci = { git = "https://github.com/namib-project/rust-uci.git", rev = "3e7b6153b6df92b45428c32bb6461756563deecb", optional = true }
+rust-uci = { git = "https://github.com/Lochnair/rust-uci.git", rev = "fcfedd204fb76928ef617bf9631b041c816e03d4", optional = true, default-features = false, }
 
 [features]
-default = ["toml"]
+default = ["toml", "uci-vendored"]
 toml = ["config/toml"]
 uci = ["dep:rust-uci"]
+uci-vendored = ["uci", "rust-uci/vendored"]