restructure project into a virtual manifest

- remove redundant readme
- de-duplicate Cargo.toml information using workspace inheritance
- rename "pacdef_core" to "pacdef"
- move "crates/main/main.rs" to "crates/pacdef/src/main.rs"

crates/pacdef/Cargo.toml

@@ -0,0 +1,40 @@
+[package]
+name = "pacdef"
+description = "multi-backend declarative package manager for Linux"
+version = "1.6.0"
+
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+readme.workspace = true
+keywords.workspace = true
+categories.workspace = true
+
+[dependencies]
+anyhow = "1.0"
+clap = "4.5"
+const_format = { version = "0.2", default-features = false }
+path-absolutize = "3.1"
+regex = { version = "1.10", default-features = false, features = ["std"] }
+termios = "0.3"
+walkdir = "2.5"
+libc = "0.2"
+
+serde = "1.0"
+serde_derive = "1.0"
+serde_json = "1.0"
+serde_yaml = "0.9"
+
+pacdef_macros.workspace = true
+
+# backends
+alpm = { version = "3.0", optional = true }
+rust-apt = { version = "0.7", optional = true }
+
+[dev-dependencies]
+rstest = "0.19"
+
+[features]
+default = []
+arch = ["dep:alpm"]
+debian = ["dep:rust-apt"]