fix: use [dependencies.compat] for non-modular deps

lua (C library) and gtest are compat (non-modular) packages in
mcpp-index. Declare them under [dependencies.compat] /
[dev-dependencies.compat] subtables so mcpp resolves the correct
namespace ("compat") instead of the default ("mcpp") namespace.

Required for mcpp 0.0.10+ namespace-aware dependency pipeline.

Author: Sunrisepeak

mcpp.toml

@@ -12,8 +12,8 @@ path = "src/capi/lua.cppm"
 [targets.capi-lua]
 kind = "lib"
 
-[dependencies]
+[dependencies.compat]
 lua = "5.4.7"
 
-[dev-dependencies]
+[dev-dependencies.compat]
 gtest = "1.15.2"