restore features (can't use cargo build directly)

Author: acheong08

Cargo.toml

@@ -9,10 +9,15 @@ name = "tiktoken_core"
 crate-type = ["cdylib"]
 
 [dependencies]
-mlua = { version = "0.9.1", features = ["serialize", "module", "lua51"] }
+mlua = { version = "0.9.1", features = ["serialize", "module"] }
 # tiktoken dependencies
 fancy-regex = "0.11.0"
 regex = "1.8.3"
 rustc-hash = "1.1.0"
 bstr = "1.5.0"
 
+[features]
+lua54 = ["mlua/lua54"]
+lua53 = ["mlua/lua53"]
+lua52 = ["mlua/lua52"]
+lua51 = ["mlua/lua51"]